Frail, but a work divineMade so fairily well,So exquisitely minute,A miracle of design.
Frail, but a work divineMade so fairily well,So exquisitely minute,A miracle of design.
Frail, but a work divineMade so fairily well,So exquisitely minute,A miracle of design.
Frail, but a work divine
Made so fairily well,
So exquisitely minute,
A miracle of design.
Yet—massed together with all the prodigality of Nature’s unsparing hand—they crown the everlasting hills; or, falling in avalanche and glacier, overwhelm the stoutest works of man; or, in vast islands of floating ice, show themselves to be
Of force to withstand, year upon year, the shockOf cataract seas that snap the three-decker’s oaken spine.
Of force to withstand, year upon year, the shockOf cataract seas that snap the three-decker’s oaken spine.
Of force to withstand, year upon year, the shockOf cataract seas that snap the three-decker’s oaken spine.
Of force to withstand, year upon year, the shock
Of cataract seas that snap the three-decker’s oaken spine.
(From theDaily News, March 11, 1869.)
Our artillerists have paid more attention of late years to the destructive properties of various forms of cannon than to the question of range. It was different when first the rifling of cannon was under discussion. Then the subject which was most attentively considered (after accuracy of fire) was the range which might possibly be attained by various improvements in the structure of rifled cannon. Many of my readers will remember how, soon after the construction of Armstrong guns had been commenced in the Government factories, a story was spread abroad of the wonderful practice which had been made with this gun at a range of seven miles. At that tremendous range, a shot had been fired into the middle of a flock of geese, according to one version of the story; but this was presently improved upon, and we were told that a bird had been singled out of the flock by the artillerists and successfully ‘potted.’ Many believed this little narrative; though some few, influenced perhaps by the consideration that a flock of geese would not be visible at a distance of seven miles, were obstinately incredulous. Presently it turned out that the Armstrong gun was incapable of throwing a shot to a distance of seven miles; so that a certain air of improbability has since attached to the narrative. Still there were not wanting those who referred to ‘Queen Anne’s pocket-pistol’—the cannon which wasable to throw shot across the Straits of Dover; and in the fulness of their faith in that mythical piece of ordnance, they refused to believe that the skill of modern artillerists was unequal to the construction of cannon even more effective.
If there are any who still believe in the powers ascribed to the far-famed ‘pocket-pistol,’ they will find their confidence in modern artillery largely shaken by the announcement that it is considered a great matter that one of Whitworth’s cannon should have thrown a shot to a distance of very nearly six miles and a half. Not only is this so, however, but it is well known that no piece of ordnance has ever flung a projectile to so great a distance since first fire-arms were invented; and it may be safely predicted that men will never be able to construct a cannon which—as far as range is concerned—will do much better than this one of Mr. Whitworth’s. The greatest range which had ever before been attained fell somewhat short of six miles. The 7-inch steel gun contrived by Mr. Lynall Thomas had flung a projectile weighing 175 lbs. to a distance of 10,075 yards; and, according to General Lefroy’s ‘Handbook of Artillery,’ that was the greatest range ever recorded. But Mr. Whitworth’s cannon has thrown a shot more than 1,000 yards farther.
Very few have any idea of the difficulties which oppose themselves to the attainment of a great range in artillery practice. It may seem, at first sight, the simplest possible matter to obtain an increase of range. Let the gun be made but strong enough tobear a sufficient charge, and range seems to be merely a question of the quantity of powder made use of. But in reality the matter is much more complicated. The artillerist has to contrive that the whole of the powder made use of shall be burned before the shot leaves the cannon, and yet that the charge shall not explode so rapidly as to burst the cannon. If he used some forms of powder, very useful for special purposes, half the charge would be blown out without doing its share of work. On the other hand, there are some combustibles (as gun-cotton and the nitrates) which burn so fast that the gun would be likely to burst before the shot could be expelled. Then, again, the shot must fit so closely that there shall be no windage, and yet not so closely as to resist too much the action of the exploding powder. Again, there is the form of the shot to be considered. A sphere is not the solid which passes most readily through a resisting medium like the air; and yet, other projectiles, which are best so long as they maintain a certain position, meet with a greater resistance when once they begin to move unsteadily. The conoid used in ordinary rifle practice, for example, passes much more freely through the air, point first, than an ordinary spherical bullet; but if the point did not travel first, as would happen but for the rifling, or even if the conoidal bullet ‘swayed about’ on its course, it would meet with more resistance than a spherical bullet. Hence the question of ‘fast or slow rifling’ has to be considered. ‘Fast rifling’ gives the greater spin, but causes more resistance to the exit ofthe shot from the barrel; with ‘slow-rifling,’ these conditions are reversed.
And then the common notion is that a cannon-ball travels in the curve called a parabola, and that artillerists have nothing to do but to calculate all about this parabola, and to deduce the range from the initial velocity according to some simple principles depending on the properties of the curve. All this is founded on a complete misapprehension of the true difficulties in the way of the problem. Only projectiles thrown with small velocity from the earth travel in parabolic paths. A cannon-ball follows a wholly different kind of curve. The resistance of the air, which seems to most persons a wholly insignificant item in the inquiry, is so enormous in the case of a cannon-ball as to become by far the most important difficulty in the way of the practical artillerist. When a 250-lb. shot is hurled with such force from a gun as to cover a range of six miles, the resistance of the air is about forty times the weight of the ball—that is, is equivalent to a weight of upwards of four tons. The range in such a case as this is but a small fraction of that which would be given by the ordinary parabolic theory.
As regards artillery practice in war, there are other difficulties in the attainment of a very extended range. Cannon meant for battering down forts cannot possibly be used in the same way that Whitworth’s was used at Shoeburyness. If the shot flung from this gun at an elevation of thirty-three degrees could have been watched, it would have been found that it fell to theearth at a much greater angle—that is, much more nearly in a perpendicular direction. On the ordinary parabolic theory, of course, the angle of fall would be the same as the angle of elevation, but under actual circumstances there is an important difference. If forts are to be battered down, however, it will not serve that they should be struck from above; our artillerists must perforce keep to the old method of pounding away at the face of the forts they attack. Therefore, an elevation which is all very well for mortars—that is, when the question merely is of flinging a bomb into a town or fortress—is utterly unsuited for ordinary artillery. With an elevation of ten degrees, Whitworth’s cannon scarcely projected the 250-lb. shot to a distance of three miles.
The progress of the modern science of gunnery certainly tends to increase the distance at which armies will engage each other. With field artillery flinging shot to a distance of two or three miles, and riflemen able to make tolerably sure practice at a distance of three-quarters of a mile, we are not likely often to hear of hand-to-hand conflicts in future warfare. The use of breech-loaders will also tend to the same effect. Hitherto we have scarcely had experience of the results which these changes are to produce on modern warfare. At Sadowa breech-loaders did not encounter breech-loaders, and it was easy for the victors in that battle to come to close quarters with their enemies. But in a battle where both sides are armed with breech-loaders, we shall probably see another sort ofaffair altogether. The bayonet will be an almost useless addition to the soldier’s arms; a charge of cavalry upon well-armed infantry will be almost as hopeless as the famous Balaclava charge; and the artillery on either side will have to play a game at long bowls. I venture to anticipate that the first great European war will introduce a total change into the whole system of warlike manœuvres.14
(From theDaily News, November 1868.)
The Royal Commission on the Law of Marriage has attracted attention to many singular and instructive results of modern statistical inquiry. Not the least important of these is the apparent influence of marriage on the death-rate. For several years it has been noticed by statisticians that the death-rate of unmarried men is considerably higher than the death-rate of married men and widowers. I believe that Dr. Stark, Registrar-General for Scotland, was one of the first to call attention to this peculiarity, as evidenced by the results of two years’ returns for Scotland. But the law has since been confirmed by a far wider range of statistical inquiry. The relative proportion between the death-rates of the married and of the unmarried is not absolutely uniform in different countries, but it isfairly enough represented by the following table, which exhibits the mortality per thousand of married and unmarried men in Scotland:—
Ages.Husbands and Widowers.Unmarried.20 to 256·2612·3125 to 808·2314·9430 to 358·6515·9435 to 4011·6716·0240 to 4514·0718·3545 to 5017·0421·1850 to 5519·5426·3455 to 6026·1428·5460 to 6535·6344·5465 to 7052·9360·2170 to 7581·56102·7175 to 80117·85143·9480 to 85173·88195·40
From this table we are to understand that out of one hundred thousand married persons (including widowers) from 20 to 25 years old, 626 die in the course of each year; while out of a similar number of unmarried persons, between the same ages, no less than 1,231 die in each year. And in like manner all the other lines of the table are to be interpreted.
Commenting on the evidence supplied by the above figures, Dr. Stark stated that ‘bachelorhood is more destructive to life than the most unwholesome trades, or than residence in an unwholesome house or district, where there has never been the most distant attempt at sanitary improvement of any kind.’ And this view has been very generally accepted, not only by the public, but by professed statisticians. Yet, as a matter of fact, I believe that no such inferences can legitimately bedrawn from the above table. Dr. Stark appears to me to have fallen into the mistake, which M. Quetelet tells us is so common, of trying to make his statistics carry more weight than they are capable of bearing. It is important that the matter should be put in a just light, for the Royal Commission on the Law of Marriage has revealed no more striking fact than that of the prevalence of immature marriages, and such reasoning as Dr. Stark’s certainly cannot tend to discourage these unwise alliances. If death strikes down in five years only half as many of those who are married as of those who are unmarried between the ages of 20 and 25 (as appears from the above table), and if the proportion of deaths between the two classes goes on continually diminishing in each successive lustre (as is also shown by the above table), it seems reasonable to infer that the death-rate would be even more strikingly disproportionate for persons between the ages of fifteen and twenty than for persons between the ages of twenty and twenty-five. I believe, indeed, that if Dr. Stark had extended his table to include the former ages, the result would have been such as I have indicated. Yet few will suppose that very youthful marriages can exercise so singularly beneficial an effect.
To many Dr. Stark’s conclusion may appear to be a natural and obvioussequiturfrom the evidence upon which it is founded. Admitting the facts—and I see no reason for doubting them—it may appear at first sight that we are bound to accept the conclusion thatmatrimony is favourable to longevity. Yet the consideration of a few parallel cases will suffice to show how small a foundation the figures I have quoted supply for such a conclusion. What would be thought, for example, of any of the following inferences?—Among hot-house plants there is observed a greater variety and brilliance of colour than among those which are kept in the open air; therefore the housing of plants conduces to the splendour of their colouring. Or again: The average height of Life Guardsmen is greater than that of the rest of the male population; therefore to be a Life Guardsman conduces to tallness of stature. Or to take an example still more closely illustrative of Dr. Stark’s reasoning: The average longevity of noblemen exceeds that of untitled persons; therefore to have a title is conducive to longevity; or borrowing his words, to remain without a title ‘is more destructive to life than the most unwholesome trades, or than residence in an unwholesome house or district, where there has never been the most distant attempt at sanitary improvement of any kind.’
We know that the inference is absurd in each of the above instances, and we are able at once to show where the flaw in the reasoning lies. We know that splendid flowers are more commonly selected for housing, and that Life Guardsmen are chosen for their tallness, so that we are prevented from falling into the mistake of ascribing splendour of colour in the one instance, or tallness in the other, to the influence of causes which have nothing whatever to do with those attributes;nor is anyone likely to ascribe the longevity of our nobility to the possession of a title. Yet there is nothing in any one of the above inferences which is in reality more unsound than Dr. Stark’s inference from the mortality bills, when the latter are considered with due reference to the principles of interpretation which statisticians are bound to follow.
The fact is, that in dealing with statistics the utmost care is required in order that our inferences may not be pushed beyond the evidence afforded by our facts. In the present instance, we have simply to deal with the fact that the death-rate of unmarried men is higher than the death-rate of married men and widowers. From this fact we cannot reason as Dr. Stark has done to asimpleconclusion. All that we can do is to show that one ofthreeconclusions must be adopted:—Either matrimony is favourable (directly or indirectly) to longevity, in a degree sufficient wholly to account for the observed peculiarity; or a principle of selection—the effect of which is such as, on the whole, to fill the ranks of married men from among the healthier and stronger portion of the community—operates in a sufficient degree to account wholly for the observed death-rates; or lastly, the observed death-rates are due to the combination, in some unknown proportion, of the two causes just mentioned.
No reasonable doubt can exist, as it seems to me, that the third is the true conclusion to be drawn from the evidence supplied by the mortality bills. Unfortunately, the conclusion thus deduced is almost valueless,because we are left wholly in doubt as to the proportion which subsists between the effects to be ascribed to the two causes thus shown to be in operation.
It scarcely required the evidence of statistics to prove that each cause must operate to some extent.
It is perfectly obvious, on the one hand, that although hundreds of men who would be held by insurance companies to be ‘bad lives’ may contract marriage, yet on the whole a principle of selection is in operation which must tend to bring the healthier portion of the male community into the ranks of the married, and to leave the unhealthier in the state of bachelorhood. A little consideration will show also that, on the whole, the members of the less healthy trades, very poor persons, habitual drunkards, and others whose prospects of long life are unfavourable, must (on the average of a large number) be more likely to remain unmarried than those more favourably situated. Another fact drawn from the Registrar-General’s return suffices to prove the influence of poverty on the marriage-rate. I refer to the fact that marriages are invariably more numerous in seasons of prosperity than at other times. Improvident marriages are undoubtedly numerous, but prosperity and adversityhavetheir influence, and that influence not unimportant, on the marriage returns.
On the other hand, it is perfectly obvious that the life of a married man is likely to be more favourable to longevity than that of a bachelor. The mere fact that a man has a wife and family depending uponhim will suffice to render him more careful of his health, less ready to undertake dangerous employments, and so on; and there are other reasons which will occur to everyone for considering the life of a married man better (in the sense of the insurance companies) than that of a bachelor. In fact, while we are compelled to reject Dr. Stark’s statement that ‘bachelorhood is more destructive to life than the most unwholesome trades, or than residence in an unwholesome house or district, where there has never been the most distant attempt at sanitary improvement of any kind,’ we may safely accept his opinion that statistics ‘prove the truth of one of the first natural laws revealed to man—“It is not good that man should live alone.”’
(From theDaily News, October 17, 1868.)
At the close of the war with Tippoo Sahib, Major Lambton planned the triangulation of the country lying between Madras and the Malabar coast, a district which had been roughly surveyed, during the progress of the war, by Colonel Mackenzie. The Duke of Wellington gave his approval to the project, and his brother, the Governor-General of India, and Lord Clive (son of the great Clive), Governor of Madras, used their influence to aid Major Lambton in carrying out his design. The only astronomical instrument madeuse of by the first survey party was one of Ramsden’s zenith-sectors, which Lord Macartney had placed in the hands of Dinwiddie, the astronomer, for sale. A steel chain, which had been sent with Lord Macartney’s embassy to the Emperor of China and refused, was the only apparatus available for measuring.
Thus began the great Trigonometrical Survey of India, a work whose importance it is hardly possible to over-estimate. Conducted successively by Colonel Lambton, Sir George Everest, Sir Andrew Waugh, and Lieut.-Col. Walker (the present superintendent), the trigonometrical survey has been prosecuted with a skill and accuracy which renders it fairly comparable with the best work of European surveyors. But to complete in this style the survey of the whole of India would be the work of several centuries. The trigonometrical survey of Great Britain and Ireland has been already more than a century in progress, and is still unfinished. It can, therefore, be imagined that the survey of India—nearly ten times the size of the British Isles, and presenting difficulties a hundredfold greater than those which the surveyor in England has to encounter—is not a work which can be quickly completed.
But the growing demands of the public service have rendered it imperatively necessary that India should be rapidly and completely surveyed. This necessity led to the commencement of the Topographical Survey of India, a work which has been pushed forward at a surprising rate during the past few years. My readersmay form some idea of the energy with which the survey is in progress, from the fact that Colonel Thuillier’s Report for the season 1866-67 announces the charting of an area half as large as Scotland, and the preparatory triangulation of an additional area nearly half as large as England.
In a period of thirty years, with but few surveying parties at first, and a slow increase in their number, an area of 160,000 square miles has been completed and mapped by the topographical department. The revenue surveyors have also supplied good maps (on a similar scale) of 364,000 square miles of country during the twenty years ending in 1866. Combining these results, we have an area of 524,000 square miles, or upwards of four times that of Great Britain and Ireland. For all this enormous area the surveyors have the records in a methodical and systematic form, fit for incorporation in the atlas of India. Nor does this estimate include the older revenue surveys of the North-western Provinces which, for want of proper supervision in former years, were never regularly reduced. The records of these surveys were destroyed in the Mutiny—chiefly in Hazaumbaugh and the south-western frontier Agency. The whole of these districts remain to be gone over in a style very superior to that of the last survey.
The extent of the country which has been charted may lead to the impression that the survey is little more than a hasty reconnaissance. This, however, is very far indeed from being the case. The preliminary triangulation, which is the basis of the topographical survey, isconducted with extreme care. In the present Report, for instance, we find that the discrepancies between the common sides of the triangles-in other words, the discrepancies between the results obtained by different observers-are in some cases less than one-tenth of an inch per mile; in others they are from one inch to a foot per mile; and in the survey of the Cossyah and Garrow Hills, where observations had to be taken to large objects, such as trees, rocks, &c., with no defined points for guidance, the results differ by as much as twenty-six inches per mile. These discrepancies must not only be regarded as insignificant in themselves, but must appear yet more trifling when it is remembered that they are not cumulative, inasmuch as the preliminary triangulation is itself dependent on the great trigonometrical survey.
Let us understand clearly what are the various forms of survey which are or have been in progress in India. There are three forms to be considered:—(1) The Great Trigonometrical Surveys; (2) The Revenue Surveys; and (3) the Topographical Surveys.
Great trigonometrical operations are extended in a straight course from one measured base to another. Every precaution which modern skill and science can suggest is taken in the measurement of each base-line, and in the various processes by which the survey is extended from one base-line to the other. The accuracy with which work of this sort is conducted may be estimated from the following instance. During the progress of the Ordnance Survey of Great Britain andIreland, a base-line nearly eight miles long was measured near Lough Foyle, in Ireland, and another nearly seven miles long on Salisbury Plain. Trigonometrical operations were then extended from Lough Foyle to Salisbury Plain, a distance of about 340 miles; and the Salisbury base-line was calculated from the observations made over this long arc.The difference between the measured and calculated values of the base-line was less than five inches!As we have stated, the trigonometrical survey of India will bear comparison with the best work of our surveyors in England.
A revenue survey is prosecuted for the definition of the boundaries of estates and properties. The operations of such a survey are therefore carried on conformably to those boundaries.
The topographical survey of a country is defined by Sir A. Scott Waugh to imply ‘the measurement and delineation of the natural features of a country, and the works of man thereon, with the object of producing a complete and sufficiently accurate map. Being free from the trammels of boundaries of properties, the principal lines of operations must conform to the features of the country, and objects to be surveyed.’
The only safe basis for the topographical survey of a country is a system of accurate triangulation. And where the extent of country to be surveyed is large, there will always be a great risk of the accumulation of error in the triangulation itself; which must, therefore, be made to depend on the accurate results obtained by the great trigonometrical operations. In order to securethis result, fixed stations are established in the vicinity of the great trigonometrical series. Where this plan cannot be adopted, a network of large symmetrical triangles is thrown over the district to be surveyed, or boundary series of triangles are carried along the outline of the district or along convenient internal lines. The former of these methods is applicable to a hilly district, the latter to a flat country.
When the district to be surveyed has been triangulated, the work of filling-in the topographical details is commenced. Each triangle being of moderate extent, with sides from three to five miles in length, and the angular points being determined, as we have seen, with great exactness, it is evident that no considerable error can occur in filling-in the details. Hence, methods can be adopted in the final topographical work which would not be suitable for triangulation. The triangles can either be ‘measured up,’ or the observer may traverse from trigonometrical point to point, taking offsets and intersections; or, lastly, he may make use of the plane table. The two first methods require little comment; but the principle of plane-tabling enters so largely into Indian surveying, that this notice would be incomplete without a brief account of this simple and beautiful method.
The plane-table is a flat board turning on a vertical pivot. It bears the chart on which the observer is planning the country. Suppose, now, that two pointsAandBare determined, and that we require to mark in the position of a third pointC:—It is clear that if weobserved with a theodolite the anglesA B CandB A C, we might lay these down on the chart with a protractor, and so the position ofCwould be determined, with an accuracy proportioned to the care with which the observations were made and the corresponding constructions applied to the chart. But in ‘plane-tabling’ a more direct plan is adopted. A ruler bearing sights, resembling those of a rifle, is so applied that the edge passing through the pointAon the chart (the observer being situated at the real stationA) passes through the pointBon the chart, the line of sight passing through the real stationB. The table being fixed in the position thus obtained, the ruler is next directed so that its edge passes throughA, while the line of sight points toC. A line is now ruled with a pencil throughAtowardsC. In a similar manner, the table having been removed to the stationB, a pencil line is drawn through the pointBon the chart towardsC. The two lines thus drawn determine by their intersection the place ofCon the chart.
The above is only one instance of the modes in which a plane-table can be applied; there are several others. Usually the magnetic compass is employed to fix the position of the table in accordance with the true bearing of the cardinal points. Also the bearings of several points are taken around each station; and thus a variety of tests of the correctness of the work become applicable. Into such details as these I need not here enter. It is sufficient that my readers should have been enabled to recognise the simple principles on whichplane-tabling depends, and the accuracy with which (when suitable precautions are taken) it can be applied as a method of observation subsidiary to the ordinary trigonometrical processes.
‘A hilly country,’ says Sir A. Waugh, ‘offers the fairest field for the practice of plane-table surveys, and the more rugged the surface the greater will be the relative advantages and facilities this system possesses over the methods of actual measurement. On the other hand, in flat lands the plane-table works at a disadvantage, while the traverse system is facilitated. Consequently, in such tracts, the relative economy of the two systems does not offer so great a contrast as in the former. In closely wooded or jungly tracts, all kinds of survey operations are prosecuted at a disadvantage; but in such localities, the commanding points must be previously cleared for trigonometrical operations, which facilitates the use of the table.’
In whatever way the topographical details have been filled in, a rigorous system of check must be applied to the work. The system adopted is that of running lines across ground that has been surveyed. This is done by the head of the party or by the chief assistant-surveyor. A sufficient number of points are obtained in this way for comparison with the work of the detail surveyors; and when the discrepancies exceed certain limits, the work in which they appear is rejected. Owing to the extremely unhealthy, jungly, and rugged nature of the ground in which nearly all the Indian surveys have beenprogressing, it has not always been found practicable to check by regularly chained lines. There are, however, other modes of testing plane-table surveys, and as these entail less labour and expense in hilly and jungly tracts, and are quite as effective if thoroughly carried out, they have been adopted generally, while the measured routes or check-lines have only been pursued under more favourable conditions. Colonel Thuillier states that ‘the inspection of the work of every detailed surveyor in the field has been rigorously enforced, and the work of the field season is not considered satisfactory or complete unless this duty has been attended to.’
The rules laid down to insure accuracy in the survey are—first, that the greatest possible number of fixed points should be determined by regular triangulation; secondly, that the greatest possible number of plane-table fixings should be made use of within each triangle; and lastly, that eye-sketching should be reduced to a minimum. If these rules are well attended to, the surveyor can always rely on the value of the work performed by his subordinates. But all these conditions cannot be secured in many parts of the ground allotted to the several topographical parties owing to the quantity of forest land and the extremely rugged nature of the country. Hence arises the necessity for test-lines to verify the details, or for some vigorous system of check; and this is more especially the case where native assistants are employed.
So soon as the country has been accurately planned, the configuration of the ground has to be sketched up. This process is the end and aim of all the preceding work.
The first point attended to is the arterial system, or water drainage, constituting the outfall of the country; whence are deduced the lines of greatest depression of the ground. Next the watersheds or ridges of hills are traced in, giving the highest level. Lastly, the minor or subordinate features are drawn in with the utmost precision attainable. ‘The outlines of table-land should be well defined,’ says Sir A. Waugh, ‘and ranges of hills portrayed with fidelity, carefully representing the watersheds ordivortia aquarum, the spurs, peaks, depressions or saddles, isthmuses or connecting-links of separate ranges, and other ramifications. The depressed points and isthmuses are particularly valuable, as being either the sites of ordinary passes or points which new roads should conform to.’
And here we must draw a distinction between survey and reconnaissance. It is absolutely necessary in making a survey that the outlines of ground as defined by ridges, water-courses, and feet of hills should be rigorously fixed by actual observation and careful measurement. In reconnoitring, more is trusted to the eye.
The scale of the Indian topographical survey is that of one inch per mile; the scale of half an inch per mile being only resorted to in very denselywooded or jungly country, containing a few inhabitants and little cultivated, or where the climate is so dangerous that it is desirable to accelerate the progress of the survey.
On the scale of one inch per mile the practised draughtsman can survey about five square miles of average country per day. In intricate ground, intersected by ravines or covered by hills of irregular formation, the work proceeds much more slowly; on the other hand, in open and nearly level country, or where the hills have simple outlines, the work will cost less and proceed more rapidly. On the scale of one inch per mile all natural features (such as ravines or watercourses) more than a quarter of a mile in length can be clearly represented. Villages, towns, and cities can be shown, with their principal streets and roads, and the outlines of fortifications. The general figure and extent of cultivated, waste, and forest lands can be delineated with more or less precision, according to their extent. Irrigated rice-lands should be distinctly indicated, since they generally exhibit the contour of the ground.
The relative heights of hills and depths of valleys should be determined during the course of a topographical survey. These vertical elements of a survey can be ascertained by trigonometrical or by barometrical observations, or by a combination of both methods. ‘The barometer,’ says Sir A. Waugh, ‘is more especially useful for determining the level of low spots from which the principal trigonometricalstations are invisible. In using this instrument, however, in combination with the other operations, the relative differences of heights are to be considered the quantities sought, so that all the results may be referable to the original trigonometrical station. The height above the sea-level of all points coming under any of the following heads is especially to be determined, for the purpose of illustrating the physical relief of the country:—
‘1st. The peaks and highest points of ranges.
‘2nd. All obligatory points required for engineering works, such as roads, drainage, and irrigation, viz.:—the highest points or necks of valleys; the lowest depressions or passes in ranges; the junctions of rivers, anddébouchementsof rivers from ranges; the height of inundation-level, at moderate intervals of about three miles apart.
‘3rd. Principal towns or places of note.’
Of the various methods employed to indicate the steepness of slope, that of eye-contouring seems alone to merit special comment. In true contouring, regular horizontal lines, at fixed vertical intervals, are traced over a country, and plotted on to the maps. This is an expensive and tedious process, whereas eye-contouring is easy, light, and effective. On this system all that is necessary is that the surveyor should consider what routes persons moving horizontally would pursue. He draws lines on his chart approximating as closely as possible to these imaginary lines. It is evident that when lines are thus drawn for different vertical elevations, the resulting shading will be dark or light, according as the slope is steep or gentle. This method of shading affords scope as well for surveying skill as for draughtsmanship.
(FromOnce a Week, May 1, 1869.)
I have always been puzzled to imagine how the ‘nine-and-twenty knights of fame,’ described in the ‘Lay of the Last Minstrel,’ managed to ‘drink the red wine through the helmet barr’d.’ But in nature we meet with animals which seem almost as inconveniently armed as those chosen knights, who
. . . quitted not their armour bright,Neither by day nor yet by night.
. . . quitted not their armour bright,Neither by day nor yet by night.
. . . quitted not their armour bright,Neither by day nor yet by night.
. . . quitted not their armour bright,
Neither by day nor yet by night.
Amongst such animals the sword-fish must be recognised as one of the most uncomfortably-armed creatures in existence. The shark has to turn on his back before he can eat, and the attitude scarcely seems suggestive of a comfortable meal. But the sword-fish can hardly even by that arrangement get his awkwardly projecting snout out of the way. Yet doubtless this feature, which seems so inconvenient, is of great value to Xiphias. In some way as yet unknown it enables him to get his living. Whether he first kills some one of his neighbours with this instrument, and then eats him at his leisure, or whether he plunges it deep intothe larger sort of fish, and attaching himself to them in this way, sucks nutriment from them while they are yet alive, is not known to naturalists. Certainly, he is fond of attacking whales, but this may result not so much from gastronomic tastes as from a natural antipathy—envy, perhaps, at their superior bulk. Unfortunately for himself, Xiphias, though cold-blooded, seems a somewhat warm-tempered animal; and, when he is angered, he makes a bull-like rush upon his foe, without always examining with due care whether he is likely to take anything by his motion. And when he happens to select for attack a stalwart ship, and to plunge his horny beak through thirteen or fourteen inches of planking, with perhaps a stout copper sheathing outside it, he is apt to find some little difficulty in retreating. The affair usually ends by his leaving his sword embedded in the side of the ship. In fact, no instance has ever been recorded of a sword-fish recovering his weapon (if I may use the expression) after making a lunge of this sort. Last Wednesday the Court of Common Pleas—rather a strange place, by-the-bye, for inquiring into the natural history of fishes—was engaged for several hours in trying to determine under what circumstances a sword-fish might be able to escape scot-free after thrusting his snout into the side of a ship, The gallant ship ‘Dreadnought,’ thoroughly repaired, and classed A 1 at Lloyd’s, had been insured for 3,000l.against all the risks of the seas. She sailed on March 10, 1864, from Colombo, for London. Three days later, the crew,while fishing, hooked a sword-fish. Xiphias, however, broke the line, and a few moments after leaped half out of the water, with the object, it would seem, of taking a look at his persecutor, the ‘Dreadnought.’ Probably he satisfied himself that the enemy was some abnormally large cetacean, which it was his natural duty to attack forthwith. Be this as it may, the attack was made, and at four o’clock the next morning the captain was awakened with the unwelcome intelligence that the ship had sprung a leak. She was taken back to Colombo, and thence to Cochin, where she was hove down. Near the keel was found a round hole, an inch in diameter, running completely through the copper sheathing and planking.
As attacks by sword-fish are included among sea risks, the insurance company was willing to pay the damages claimed by the owners of the ship, if only it could be proved that the hole had really been made by a sword-fish. No instance had ever been recorded in which a sword-fish had been able to withdraw his sword after attacking a ship. A defence was founded on the possibility that the hole had been made in some other way. Professor Owen and Mr. Frank Buckland gave their evidence; but neither of them could state quite positively whether a sword-fish which had passed its beak through three inches of stout planking could withdraw without the loss of its sword. Mr. Buckland said that fish have no power of ‘backing,’ and expressed his belief that he could hold a sword-fish by the beak; but then he admitted that the fish had considerablelateral power, and might so ‘wriggle its sword out of a hole.’ And so the insurance company will have to pay nearly six hundred pounds because an ill-tempered fish objected to be hooked, and took its revenge by running full tilt against copper sheathing and oak planking.
(From theDaily News, December 11, 1868.)
As recent colliery explosions have attracted a considerable amount of attention to the principle of the safety-lamp, and questions have arisen respecting the extent of the immunity which the action of this lamp secures to the miner, it may be well for me briefly to point out the true qualities of the lamp.
In the Davy lamp a common oil-light is surrounded by a cylinder of wire-gauze. When the air around the lamp is pure the flame burns as usual, and the only effect of the gauze is somewhat to diminish the amount of light given out by the lamp. But so soon as the air becomes loaded with the carburetted hydrogen gas generated in the coal-strata, a change takes place. The flame grows larger and less luminous. The reason of the change is this:—The flame is no longer fed by the oxygen of the air, but is surrounded by an atmosphere which is partly inflammable; and the inflammable part of the gas, sofast as it passes within the wire cylinder, is ignited and burns within the gauze. Thus the light now given out by the lamp is no longer that of the comparatively brilliant oil flame, but is the light resulting from the combustion of carburetted hydrogen, or ‘fire damp,’ as it is called; and every student of chemistry is aware that the flame of this gas has very little illuminating power.
So soon as the miner sees the flame thus enlarged and altered in appearance he should retire. But it is not true that explosion would necessarily follow if he did not do so. The danger is great because the flame within the lamp is in direct contact with the gauze, and if there is any defect in the wire-work, the heat may make for itself an opening which—though small—would yet suffice to enable the flame within the lamp to ignite the gas outside. So long, however, as the wire-gauze continues perfect, even though it become red-hot, there will be no explosion. No authority is required to establish this point, which has been proved again and again by experiment; but I quote Professor Tyndall’s words on the subject to remove some doubts which have been entertained on the matter. ‘Although a continuous explosive atmosphere,’ he says,‘may extend from the air outside through the meshes of the gauze to the flame within, ignition is not propagated across the gauze. The lamp may be filled with an almost lightless flame; still explosion does not occur. A defect in the gauze, the destruction of the wire at any point by oxidation hastened by the flame playing against it, would cause explosion;’ and so on. It need hardly be said, however, that, imprudent as miners have often been, no miner would remain where his lamp burned with the enlarged flame indicative of the presence of fire-damp. The lamp should also be at once extinguished.
But here we touch on a danger which undoubtedly exists, and—so far as has yet been seen—cannot be guarded against by any amount of caution. Supposing the miner sought to extinguish the lamp by blowing it out, an explosion would almost certainly ensue, since the flame can be forced mechanically through the meshes, though it will not pass through them when it is burning in the ordinary way. Now of course no miner who had been properly instructed in the use of the safety-lamp would commit such a mistake as this. But it happens, unfortunately, that sometimes the fire-damp itself forces the flame of the lamp through the meshes. The gas frequently issues with great force from cavities in the coal (in which it has been pent up), when the pick of the miner breaks an opening for it. In these circumstances an explosion is inevitable, if the issuing stream of gas happen to be directed full upon the lamp. Fortunately, however, this is a contingency which does not often arise. It is one of those risks of coal-mining which seem absolutely unavoidable by any amount of care or caution. It would be well if it were only such risks as these that the miner had to face.
Another peculiarity sometimes noticed when there is a discharge of fire-damp is worth mentioning. It happens, occasionally, that the light will be put out owing to the absolute exclusion of air from the lamp. This, however, can only happen when the gas issues in so large a volume that the atmosphere of the pit becomes irrespirable.
With the exception of the one risk which we have pointed out above, the Davy lamp may be said to be absolutely safe. It is necessary, however, that caution and intelligence should be exhibited in its use. On this point Professor Tyndall remarks that unfortunately the requisite intelligence is not often possessed nor the requisite caution exercised by the miner, ‘and the consequence is that even with the safety-lamp, explosions still occur.’ And he suggests that it would be well to exhibit to the miner in a series of experiments the properties of the valuable instrument which has been devised for his security. ‘Mere advice will not enforce caution,’ he says; ‘but let the miner have the physical image of what he is to expect clearly and vividly before his mind, and he will find it a restraining and monitory influence long after the effect of cautioning words has passed away.’
A few words on the history of the invention may be acceptable. Early in the present century a series of terrible catastrophes in coal mines had excited the sympathy of enlightened and humane persons throughout the country. In the year 1813, a society was formed at Sunderland to prevent accidents in coalmines or at least to diminish their frequency, and prizes were offered for the discovery of new methods of lighting and ventilating mines. Dr. William Reid Clanny, of Bishopwearmouth, presented to this society a lamp which burnt without explosion in an atmosphere heavily loaded with fire-damp; for which invention the Society of Arts awarded him a gold medal. The Rev. Dr. Gray called the attention of Sir Humphry Davy to the subject, and that eminent chemist visited the coal mines in 1815 with the object of determining what form of lamp would be best suited to meet the requirements of the coal miners. He invented two forms of lamp before discovering the principle on which the present safety-lamps are constructed. This principle—the property, namely, that flame will not pass through small apertures—had been, we believe, discovered by Stephenson, the celebrated engineer, some time before; and a somewhat angry controversy took place respecting Davy’s claim to the honour of having invented the safety-lamp. It seems admitted, however, by universal consent, that Davy’s discovery of the property above referred to was made independently, and also that he was the first to suggest the idea of using wire-gauze in place of perforated tin.
In comparing the present frequency of colliery explosions with what took place before the invention of the safety-lamp, we must take into consideration the enormous increase in the coal trade since the introduction of steam machinery. The number ofminers now engaged in our coal mines is far in excess of the number employed at the beginning of the present century. Thus accidents in the present day are at once more common on account of the increased rapidity with which the mines are worked, and when they occur there are more sufferers; so that the frequency of colliery explosions in the opening years of the present century and the number of deaths resulting from them, are in reality much more significant than they seem to be at first sight. But even independently of this consideration, the record of the colliery accidents which took place at that time is sufficiently startling. Seventy-two persons were killed in a colliery at North Biddick at the commencement of the present century. Two explosions in 1805, at Hepburn and Oxclose, left no less than forty-three widows and 151 children unprovided for. In 1808, ninety persons were killed in a coal-pit at Lumley. On May 24, 1812, ninety-one persons were killed by an explosion at Felling Colliery, near Gateshead. And many more such accidents might readily be enumerated.
(From theDaily News, December 4, 1868.)
A microscopist, Mr. Dancer, F.R.A.S., has been examining the dust of our cities. The results are not pleasing. We had always recognised city dust as a nuisance, and had supposed that it derived the peculiar grittiness and flintiness of its structure from the constant macadamizing of city roads. But it now appears that the effects produced by dust, when, as is usual, it finds its way to our eyes, our nostrils, and our throats, are as nothing compared with the mischief it is calculated to produce in a more subtle manner. In every specimen examined by Mr. Dancer animal life was abundant. But the amount of ‘molecular activity’—such is the euphuism under which what is exceedingly disagreeable to contemplate is spoken about—is variable according to the height at which the dust is collected. And of all heights which these molecular wretches could select for the display of their activity, the height of five feet is that which has been found to be the favourite. Just at the average height of the foot-passenger’s mouth these moving organisms are always waiting to be devoured and to make us ill. And this is not all. As if animal abominations were insufficient, a large proportion of vegetable matter also disports itself in the light dust of our streets. The observations show that in thoroughfares where there are many animals engaged in the traffic, the greater part of the vegetable matter thus floating about‘consists of what has passed through the stomachs of animals,’ or has suffered decomposition in some way or other. This unpleasing matter, like the ‘molecular activity,’ floats about at a height of five feet, or thereabouts.
After this, one begins to recognise the manner in which some diseases propagate themselves. What had been mysterious in the history of plagues and pestilences seems to receive at least a partial solution. Take cholera, for example. It has been shown by the clearest and most positive evidence that this disease is not propagated in any way save one—that is, by the actual swallowing of the cholera poison. In Professor Thudichum’s masterly paper on the subject in the ‘Monthly Microscopical Journal,’ it is stated that doctors have inhaled a full breathing from a person in the last stage of this terrible malady without any evil effects. Yet the minutest atom of the cholera poison received into the stomach will cause an attack of cholera. A small quantity of this matter drying on the floor of the patient’s room, and afterwards caused to float about in the form of dust, would suffice to prostrate a houseful of people. We can understand, then, how matter might be flung into the streets, and, after drying, its dust be wafted through a whole district, causing the death of hundreds. One of the lessons to be learned from these interesting researches of Mr. Dancer is clearly this, that the watering-cart should be regarded as one of the most important of our hygienic institutions. Supplemented by careful scavengering, itmight be effective in dispossessing many a terrible malady which now holds sway from time to time over our towns.
(From theDaily News, March 6, 1869.)
On the outskirts of the ever-widening circle lighted up by science there is always a border-land wherein superstition holds sway. ‘The arts and sciences may drive away the vulgar hobgoblin of darker days; but they bring with them new sources of illusion. The ghosts of old could only gibber; the spirits of our day can read and write, and play on divers musical instruments, and quote Shakespeare and Milton. It is not, therefore, altogether surprising to learn that they can take photographs also. You go to have your photograph taken, we will suppose, desiring only to see your own features depicted in thecarte; and lo! the spirits have been at work, and a photographic phantom makes its appearance beside you. It is true this phantom is of a hazy and dubious aspect: the ‘dull mechanic ghost’ is indistinct, and may be taken for anyone. Still, it is not difficult for the eye of fancy to trace in it the lineaments of some departed friend, who, it is to be assumed, has come to be photographed along with you. In fact, photography, according to the spiritualist, resembles what Byron called—