Fig. 25.
Fig. 25.
During the previous summer, I made the following experiments, upon a line of 33 miles, of number 17 copper wire, with a battery of 50 pairs. In this case, I used a small steelyard, with weights, with which I was enabled to weigh, with a good degree of accuracy, the greater magnetic forces, but not the lesser, yet sufficiently approximating the recent results to confirm the law in question.
and each successive addition of two miles, up to 33, still gave an attractive and lifting power of one-eighth of an ounce.
Curve from these Results.
Fig. 26.
Fig. 26.
A great irregularity is seen between the 10th and 12th miles, which is due, undoubtedly, to a deficiency of accuracy in the weighing apparatus. I take pleasure in sending you the following calculation of the law of the conducting power of wires, for which I am indebted to my friend Prof. Draper, of the New York City University.
On the Law of the Conducting Power of Wires.By John W. Draper, M. D. &c. &c.
It has been objected, that if the conducting power of wires, for electricity was inversely as their length, and directly as their section, the transmission of telegraphic signals, through long wires, could not be carried into effect, and even the galvanic multiplier, which consists, essentially, of a wire making several convolutions round a needle, could have no existence. This last objection was first brought forward by Prof. Ritchie, of the University of London, as an absolute proof, that the law referred to is incorrect. There is, however, an exceedingly simple method of proving that signals may be despatched through very long wires, and that the galvanic multiplier, so far from controverting the law in question, depends for its very existence upon it.Assuming the truth of the law of Lenz, thequantitiesof electricity which can be urged by a constant electromotoric source through a series of wires, the lengths of which constitute an arithmetical ratio, will always be in a geometrical ratio. Now the curve whose ordinates and abscissas bear this relation to each other, is the logarithmic curve whose equation isaʸ=x.1st. If we suppose the base of the system, which the curve under discussion represents, be greater than unity, the values ofytaken betweenx = 0, andx = 1, must be all negative.2d. By takingy = 0, we find that the curve will intersect the axis of thex’s, at a distance from the origin, equal to unity.3d. By makingx = 0, we findyto be infinite and negative. Now, these are the properties of the logarithmic curve, which furnish an explanation of the case in hand. Assuming that thex’s represent the quantities of electricity, and they’s the lengths of the wires, we perceive at once, that those parts of the curve which we have to consider, lie wholly in the fourth quadrant, where the abscissas are positive and the ordinates negative. When, therefore, the battery current passes without the intervention of any obstructing wire, its value is equal to unity. But, as successive lengths of wire are continually added, the quantities of electricity passing, undergo a diminution, at first rapid, and then more and more slow. And it is not until the wire becomes infinitely long that it ceases to conduct at all; for the ordinatey, whenx = 0, is an asymptote to the curve. In point of practice, therefore, when a certain limit is reached, the diminution of the intensity of the forces becomesvery small, whilst the increase in the lengths of the wire is vastly great. It is, therefore, possible to conceive a wire to be a million times as long as another, and yet, the two shall transmit quantities of electricity not perceptibly different, when measured by a delicate galvanometer. But, under these circumstances, if the long wire be coiled, so as to act as a multiplier, its influence on the needle will be inexpressibly greater than the one so much shorter than it. Further, from this we gather that for telegraphic despatches, with a battery of given electromotoric power, when a certain distance is reached, the diminution of effect for an increased distance becomes inappreciable.
It has been objected, that if the conducting power of wires, for electricity was inversely as their length, and directly as their section, the transmission of telegraphic signals, through long wires, could not be carried into effect, and even the galvanic multiplier, which consists, essentially, of a wire making several convolutions round a needle, could have no existence. This last objection was first brought forward by Prof. Ritchie, of the University of London, as an absolute proof, that the law referred to is incorrect. There is, however, an exceedingly simple method of proving that signals may be despatched through very long wires, and that the galvanic multiplier, so far from controverting the law in question, depends for its very existence upon it.
Assuming the truth of the law of Lenz, thequantitiesof electricity which can be urged by a constant electromotoric source through a series of wires, the lengths of which constitute an arithmetical ratio, will always be in a geometrical ratio. Now the curve whose ordinates and abscissas bear this relation to each other, is the logarithmic curve whose equation isaʸ=x.
1st. If we suppose the base of the system, which the curve under discussion represents, be greater than unity, the values ofytaken betweenx = 0, andx = 1, must be all negative.
2d. By takingy = 0, we find that the curve will intersect the axis of thex’s, at a distance from the origin, equal to unity.
3d. By makingx = 0, we findyto be infinite and negative. Now, these are the properties of the logarithmic curve, which furnish an explanation of the case in hand. Assuming that thex’s represent the quantities of electricity, and they’s the lengths of the wires, we perceive at once, that those parts of the curve which we have to consider, lie wholly in the fourth quadrant, where the abscissas are positive and the ordinates negative. When, therefore, the battery current passes without the intervention of any obstructing wire, its value is equal to unity. But, as successive lengths of wire are continually added, the quantities of electricity passing, undergo a diminution, at first rapid, and then more and more slow. And it is not until the wire becomes infinitely long that it ceases to conduct at all; for the ordinatey, whenx = 0, is an asymptote to the curve. In point of practice, therefore, when a certain limit is reached, the diminution of the intensity of the forces becomesvery small, whilst the increase in the lengths of the wire is vastly great. It is, therefore, possible to conceive a wire to be a million times as long as another, and yet, the two shall transmit quantities of electricity not perceptibly different, when measured by a delicate galvanometer. But, under these circumstances, if the long wire be coiled, so as to act as a multiplier, its influence on the needle will be inexpressibly greater than the one so much shorter than it. Further, from this we gather that for telegraphic despatches, with a battery of given electromotoric power, when a certain distance is reached, the diminution of effect for an increased distance becomes inappreciable.
This useful instrument, the invention of which is based upon Oersted’s discovery of the deflection of the magnetic needle, by the action of conducting wires conveying galvanic currents, seems to have furnished to most of the inventors of telegraphs, the main spring of communication. It was a very natural suggestion, as being the most convenient and ready mode of obtaining the required motion, by making and breaking the galvanic circuit. Thus Steinheil, Wheatstone and Bain have availed themselves of thisone ideato effect that part of the telegraphic operation which may be called thegalvanic, in contradistinction to themechanicalparts, which last have varied considerably with different operators. The construction and operation of the galvanometer may be understood by reference to the figures27,28,29. A A,fig. 28, are two long coils of covered copper wire, a side view of which is shown infig. 27. These coils are connected with the binding screws, L L, attached to the frame, or box, holding the coils.Two coils are used for the convenience of allowing the pivot sustaining the magnetic needle to pass between them; one coil might be used, by leaving room enough between the wires for a socket for the pivot, but the arrangement, represented, is the most readily constructed. A side view of the instrument,figure 27, shows the arrangement of the needles, two of them being generally used to increase the operation of deflection, and to neutralize the influence of the earth’s magnetism.The pair of needles is usually denominated, anastaticneedle, or a needle without directive power; as the current traversing a conducting wire gives different directions to needles placed above and below the wire, the action upon the two needles thus placed is combined, by arranging their poles in opposite directions. When the current is in the direction indicated by the arrows infigure 27, the north pole of the needle, within the coil, is carried in a direction from you, as you face the drawing, and the north pole, without the coil, in a contrary direction. The operation upon the south pole is the reverse. Changing the direction of the galvanic current, reverses the motions. It is usual to apply the force of torsion, or of ahairspring, or of the superior weight of one extremity of the needle, to act against the deflective force of the current, and to attach a graduated scale to the instrument, fixing it between the uppermost needle and the coils as infigure 29. Instead of deflecting the needle, the coils themselves may be deflected, as in the galvanoscope of Prof. Page, invented in January, 1837, and described by him in the 33d vol. of Silliman’s Journal, page 376. The object of this contrivance was to enable him to use powerful magnets and lighter coils. This modification of the galvanoscope, Mr. Bain has preferred as the means of operating his telegraph.
Fig. 27.
Fig. 27.
Fig. 28.
Fig. 28.
Fig. 29.
Fig. 29.
It has been shown, many years since, that a magnetic needle would be drawn into and suspended within a helix, conveying a galvanic current, and that in the case of using large bar magnets, the coils or helices might be made to move over them, as in De La Rives’s rings; but in no instance, I believe, has it been recorded, or observed, that a bar of iron weighing a pound or more, could be drawn up into the helix and there sustained in the air, as it were, without support. If the helix, as shown infigure 30, be connected with from 6 to 12 pairs of Grove’s battery, the bar may be drawn up into its centre and there sustained in a vertical position by the action of the helix, forming an exceedingly interesting and paradoxical experiment.
Fig. 30.
Fig. 30.
[From the National Intelligencer.]
Among the wonderful developements of the new telegraph, one has just came to light which will be regarded in the world of science as deeply interesting. Prof. Morse suggested to the distinguished Arago, in 1839, that the electro magnetic telegraph would be the means of determining the difference of longitude between places with an accuracy hitherto unattainable. By the following letter from Capt. Charles Wilkes to Prof. Morse, it will be believed that the first experiment of the kind of which we have any knowledge, has resulted in the fulfilment of the Professor’s prediction.
Washington,June 13, 1844.My Dear Sir—The interesting experiments for obtaining the difference of longitude through your magnetic telegraph were finished yesterday and have proved very satisfactory. They resulted in placing the Battle Monument square, Baltimore, 1m, .34 sec. .868 east, of the capitol. The time of the two places was carefully obtained by transit observations. The comparisons were made through chronometers and without any difficulty. They were had in three days, and their accuracy proved in the intervals marked and recorded at both places. I have adopted the results of the last day’s observations and comparisons, from the elapsed time having been less.The difference of the former results, found in the American Almanac, is .732 of a second. After these experiments, I am well satisfied that your telegraph offers the means for determining meridian distances more accurately than was before within the power of instruments and observers.Accept my thanks, and those of Lieutenant Eld, for yourself and Mr. Vail, for your kindness and attention in affording us the facilities to obtain these results. With great respect and esteem, your friend,CHARLES WILKES.ProfessorS. F. B. Morse,Capitol, Washington.
Washington,June 13, 1844.
My Dear Sir—The interesting experiments for obtaining the difference of longitude through your magnetic telegraph were finished yesterday and have proved very satisfactory. They resulted in placing the Battle Monument square, Baltimore, 1m, .34 sec. .868 east, of the capitol. The time of the two places was carefully obtained by transit observations. The comparisons were made through chronometers and without any difficulty. They were had in three days, and their accuracy proved in the intervals marked and recorded at both places. I have adopted the results of the last day’s observations and comparisons, from the elapsed time having been less.
The difference of the former results, found in the American Almanac, is .732 of a second. After these experiments, I am well satisfied that your telegraph offers the means for determining meridian distances more accurately than was before within the power of instruments and observers.
Accept my thanks, and those of Lieutenant Eld, for yourself and Mr. Vail, for your kindness and attention in affording us the facilities to obtain these results. With great respect and esteem, your friend,
CHARLES WILKES.
ProfessorS. F. B. Morse,Capitol, Washington.
The following extract from Professor Morse’s letter to the Secretary of the Treasury, and by him submitted to the House of Representatives, Dec. 23, 1844, in relation to this interesting subject, will sufficiently illustrate it:
“In the autumn of 1842, at the request of the American Institute, I undertook to give to the public in New York a demonstration of the practicability of my telegraph, by connecting Governor’s Island with Castle Garden, a distance of a mile; and for this purpose I laid my wires properly insulated beneath the water. I had scarcely begun to operate, and had received but two or three characters, when my intentions were frustrated by the accidental destruction of a part of my conductors by a vessel, which drew them up on her anchor, and cut them off. In the moments of mortification, I immediately devised, a plan for avoiding such an accident in future, by so arranging my wires along the banks of the river as to cause the water itself to conduct the electricity across. The experiment, however, was deferred till I arrived in Washington; and on December 16, 1842, I tested my arrangement across the canal, and with success. The simple fact was thenascertained, that electricity could be made to cross a river without other conductors than the water itself; but it was not until the last autumn that I had the leisure to make a series of experiments to ascertain the law of its passage. Thefollowing diagramwill serve to explain the experiment.
Fig. 31.
Fig. 31.
A, B, C, D, are the banks of the river; N, P, are the battery; E is the electro magnet;w w, are the wires along the banks, connecting with copper plates,f,g,h,i, which are placed in the water. When this arrangement is complete, the electricity, generated by the battery, passes from the positive pole, P, to the plateh, across the river through the water to platei, and thence around the coil of the magnet, E, to platef, across the river again to plateg, and thence to the other pole of the battery, N. The numbers 1, 2, 3, 4, indicate the distance along the bank measured by the number of times of the distance across the river.
The distance across the canal is 80 feet; on August 24th, the following were the results of the experiment.
Showing that electricity crosses the river, andin quantity in proportion to the size of the plates in the water.Thedistance of the plates on the same sideof the riverfrom each otheralso affects the result. Having ascertained the general fact, I was desirous of discovering the best practical distance at which to place my copper plates, and not having the leisure myself, I requested my friend Professor Gale to make the experiments for me. I subjoin his letter and the results.
New York,November5th, 1844.My Dear Sir—I send you, herewith, a copy of a series of results, obtained with four different sized plates, as conductors to be used in crossing rivers. The batteries used were six cups of your smallest size, and one liquid used for the same throughout. I made several other series of experiments, but these I most rely on for uniformity and accuracy. You will see, from inspecting the table, that the distance along the shores should bethree times greaterthan that from shore to shore across the stream; at least, that four times the distance does not give any increase of power. I intend to repeat all these experiments under more favorable circumstances, and will communicate to you the results.Very respectfully,L. D. GALE.ProfessorS. F. B. Morse,Superintendent of Telegraphs.
New York,November5th, 1844.
My Dear Sir—I send you, herewith, a copy of a series of results, obtained with four different sized plates, as conductors to be used in crossing rivers. The batteries used were six cups of your smallest size, and one liquid used for the same throughout. I made several other series of experiments, but these I most rely on for uniformity and accuracy. You will see, from inspecting the table, that the distance along the shores should bethree times greaterthan that from shore to shore across the stream; at least, that four times the distance does not give any increase of power. I intend to repeat all these experiments under more favorable circumstances, and will communicate to you the results.
Very respectfully,L. D. GALE.
ProfessorS. F. B. Morse,Superintendent of Telegraphs.
Series of Experiments on four different sizes of plates, to wit: 1st, 56 square inches; 2d, 28 square inches; 3d, 14 square inches; and 4th, 7 square inches.Experiment 1st.—Surface of one face of the copper plate, 56 square inches; battery, Morse’s smallest, 6 cups.
Series of Experiments on four different sizes of plates, to wit: 1st, 56 square inches; 2d, 28 square inches; 3d, 14 square inches; and 4th, 7 square inches.
Experiment 1st.—Surface of one face of the copper plate, 56 square inches; battery, Morse’s smallest, 6 cups.
Note.—In all the experiments,fandgare stationary.
Experiment 2d.—Plates 28 square inches, conducted as above.
Experiment 2d.—Plates 28 square inches, conducted as above.
Experiment 3d.—Plates 14 square inches, conducted as No. 1.
Experiment 3d.—Plates 14 square inches, conducted as No. 1.
Experiment 4th.—Plates 7 square inches, conducted as No. 1.
Experiment 4th.—Plates 7 square inches, conducted as No. 1.
The distance from bank to bank, 30 inches. Depth of water, 12 inches. In experiment 4, the liquor of the batteries was very weak, exhausted towards the last; and in trials 5 and 6, the irregularities are to be attributed in part to the weak liquor, and in part to the twilight hour at which the experiments were made.
As the result of these experiments, it would seem that there may be situations in which the arrangements I have made for passing electricity across the rivers may be useful, although experience alone can determine whether lofty spars, on which the wires may be suspended, erected in the rivers, may not be deemed the most practical. The experiments made were but for a short distance; in which, however, the principle was fully proved to be correct. It has been applied under the direction of my able assistants, Messrs. Vail and Rogers, across the Susquehanna river, at Havre-de-Grace, with complete success; a distance of nearly a mile.
In order to give some idea of the accuracy with which the telegraph transmits intelligence, we here give two games of chess, as played by distinguished gentlemen in Baltimore and in Washington. The two games are selected from the seven played. The number of moves made in playing the seven games, were 686, and were transmitted without a single mistake or interruption. The Baltimoreans played with the white pieces, placed on numbers 57, 58, 59, 60, 61, 62, 63, and 64,figure 32. They were commenced November 16th, 1844. B, Baltimore; W, Washington.
Fig. 32.
Fig. 32.
The magneto electric machine was originally contrived by Mr. Saxton, soon after the announcement of the interesting discovery of Faraday, that magnetism was capable of exciting electricity. The conditions necessary for obtaining electricity in this way were, chiefly, the disturbance of magnetic forces in a bar of soft iron surrounded by coils of wire. A number of mechanical contrivances were resorted to, in order to effect this disturbance, by causing the bar of iron, thus surrounded, to approach to and recede from the poles of powerful magnets; but the ingenuity of Mr. Saxton far exceeded them all, by giving to the coils and enclosed bar a rotary movement about the poles of a U-form magnet. This instrument afforded bright sparks and strong shocks; but the currents of electricity thus obtained could not be converted to any useful purpose, as, in each half revolution of the coils, the currents were in opposite directions. In 1838, Professor Page published in Silliman’s Journal an account of an improved form of the machine, doing away with many existing objections, and furthermore rendering it at once a useful instrument, by a contrivance for conducting these opposing currents into one channel or direction, whichpart of the contrivance was called theunitrep. The current produced in this way was capable of performing the work to a certain extent, of the power developed by the galvanic battery; and the machine was found adequate to the furnishing of shocks for medical purposes, for exhibiting the decomposition of water, furnishing the elements oxygen and hydrogen at their respective poles, and producing definite electro-chemical results. These two last results could not be obtained without the aid of the unitrep. But, with this improvement, the instrument was still wanting in one property of the galvanic battery, viz. that property which chemists call quantity, or that power upon which depends its ability to magnetize, and also to heat platinum wires. This last property has been given to the machine by the recent contrivance of Professor Page. The machine, in its novel construction, under his improvement, developed what is called, by way of distinction, the current of intensity, but had a very feeble magnetizing power. By a peculiar contrivance of the coils, (not to be made public until his rights are in some way secured,) the current of quantity is obtained in its maximum, while, at the same time, the intensity is so much diminished that it gives scarcely any shock, and decomposes feebly. It has been successfully tried with the magnetic telegraph of Professor Morse, and operates equally well with the battery. It affords, by simply turning a crank attached to the machine, a constant current of galvanic electricity; and as there is no consumption of material necessary to obtain this power, it will doubtless supersede the use of the galvanic battery, which, in the event of constant employment, would be very expensive, from the waste of zinc, platinum, acids, mercury, and other materials used in its construction. It particularly recommends itself for magnetizing purposes, as it requires no knowledge of chemistry to insure the result, being merely mechanical in its action, and is always ready for action without previous preparation; the turning of a crank being the only requisite when the machine is in order. It is not liable to get out of order; does not diminish perceptibly in power when in constant use, and actually gains power when standing at rest. It will be particularly gratifying to the man of science, as it enables him to have always at hand a constant power for the investigation of its properties, without any labor of preparation. We notice among the beautiful results of this machine, that it charges an electro magnet so as to sustain a weight of 1,000 pounds, and it ignites to a white heat large platinum wires, and may be used successfully for blasting at a distance; and should Government ever adopt any such system of defence as to need the galvanic power, it must supersede the battery in that case. Professor Page demonstrates, by mathematical reasoning, that the new contrivance of the coils affords the very maximum of quantity to be obtained by magnetic excitation.
Report of Commissioner of Patents, for 1844.