ACOPIOUS LISTOFMICROSCOPIC OBJECTS.

[168]Neuere Geschichte der Missions Anstalten. 48 stück. Halle 1796.

The above remarks, it is hoped, will afford some useful hints to gentlemen intending to visit India; as well as plead in justification of those who, unacquainted with the difficulty of preserving collections in so warm a climate, have previous to their departure precipitately made promises to their friends, which for want of being realized, have too frequently exposed them to unmerited censure.

In the introductory part to our author’s list of objects inChap. X.he very justly observes, that from the nature of the subject the list must be very imperfect, &c. it is not with the vain idea of rendering that complete which he has left imperfect, and which indeed must ever remain so, that the following general list is introduced; but principally with the view of still farther assisting the tyro, and pointing out a variety of articles, that might not otherwise so readily occur to him. In most instances, I have mentioned where the objects may be sought for with a probability of success; to have described them would have exceeded my limits. The specimen here given, will convince the reader, that it would be no very difficult task, so to enlarge this list, as to constitute a volume; but, it is presumed, that in its present state it will be found sufficiently extensive, and of considerable utility. To those who are already conversant with the subject, it may prove acceptable as a kind of index to assist their memories; and to such as may be disposed to form a cabinet, it will serve the purposes of directing them in their choice of the principal objects, and exhibiting some idea of the manner in which they are to be arranged.

Many of these exhibit most beautiful objects, from the elegant variety of the colours and teints of their skins and scales

Chrysomela 12 punctata;Chrysomela asparagi;}on asparagus

Chrysomela 12 punctata;Chrysomela asparagi;

}on asparagus

Cicindela riparia;Cicindela aquatica;}on wet sandy ground

Cicindela riparia;Cicindela aquatica;

}on wet sandy ground

Dytiscus cinereus;Dytiscus sulcatus;}water

Dytiscus cinereus;Dytiscus sulcatus;

}water

[169]I have caught great numbers of these on white rose trees and rasp-berry bushes, in the vicinity of London; their smell has to me always appeared approaching nearer to that of oil of rhodium than of musk.

[170]Those who are desirous of seeing well delineated and elegantly coloured figures of a variety of curious objects among the insect class, particularly such as require investigation by the microscope, will be amply gratified by having recourse to Donovan’s History of British Insects. From the Naturalists Miscellany, by G. Shaw, M. D. F. R. & Vice Pres. L. S. numbers of beautiful subjects may likewise be selected.

Having thus enumerated a considerable variety of articles in the animal and fossile kingdoms, the only part which remains to be noticed is that of vegetables. To any person possessing but a superficial knowledge of botany, it must be obvious that this branch of natural history is extensive in the extreme; and that, consequently, to point out but a small number of such plants as form interesting objects for the microscope, would greatly extend this list, already sufficiently large; for,

“How incompetent is human effort to portray the beauties of this sublime subject! How inadequate the most descriptive talent to approximate to our view the vegetative profusion contained within the recess of nature! How limited have been our public researches! How contracted the knowledge which has been as yet obtained! What an incomprehensible store remains yet concealed, impenetrable to mortal view!”[171]

[171]Observations on the Structure and Economy of Plants, by R. Hooper, M. D., F. L. S. page 128. This work contains an ingenious display of the analogy which subsists between the animal and the vegetable kingdom.

From a source so abundant, the botanist will be under no difficulty in selecting for himself; those who have not made the science a part of their studies, will be materially assisted by having recource to the elegant figures and their descriptions in the Botanical Magazine, by W. Curtis, F. L. S. the well-known author of Flora Londinensis; and English Botany, by J. E. Smith, M. D. F. R. & Pres. L. S. published by Jas. Sowerby, F. L. S. I shall, therefore, just mention in general terms those parts of plants which are peculiarly adapted for microscopical investigation. These are as follow:

[172]The pollen or meal is a fine dust designed for the impregnation of the germen; a small quantity of this meal being put into hot water and applied to the microscope, will exhibit the bursting of the elastic covering of each grain; and the escape of the smaller atoms, which is the true farina.

Of the various classes of plants, that called cryptogamia is eminently calculated for microscopical observation; comprizing the filices, the musci, the algæ, and the fungi. On these subjects Hedwig has produced a valuable work, entitled Theoria Generationis et Fructificationis de Plantarum Cryptogamicarum, of which a new and much improved edition has just appeared, and to which for further information I refer the reader.

N. B. Those marked with an * Mr. Custance conceives prove Dr. Hill in an error, when he observed, that the pith of a shoot is not connected with the pith of the branch. See his Construction of Timber, &c. p. 103, 8vo edition.

[173]To ascertain the true configurations of salts, particular attention should be paid to obtain them genuine; it may therefore be proper to apprize the reader, that some of those above enumerated are not easily procured in that state; consequently, though they exhibit pleasing figures, yet they may not be those of the real salt purposed to be investigated. Many hundred weights of some salts are annually manufactured, and sold under names very different from what they really are. Nor is this circumstance confined to salts only: for want of botanical knowledge, preparations of different plants have been frequently sold possessed of medical properties very different from those intended. A valuable medicine, the extract of Hemlock, for instance, instead of being prepared of the conium maculatum, has been made in large quantities of the chærophyllum sylvestre, and thus administered! On this unpleasant subject I could enlarge, were it not digressing from that before us. Whilst such evils exist, need we wonder if the physician as well as the patient are often disappointed in the beneficial effects expected from the adhibition of medicines?

After having particularized so many of the works ofNATURE, let us now pay some attention to those ofART. But what an humiliating contrast shall we meet with! If our design in viewing objects by the microscope be to discover beauty, harmony, and perfection, it will be necessary to limit our inquiries to the former, happily alone sufficiently abundant; if, on the contrary, we are desirous of discovering deformity and imperfection, we must confine ourselves to the latter. Even those works of art that appear to the unassisted eye as decisive proofs of consummate skill in the workman, and which excite our admiration for their apparent neatness and accuracy, when brought to this test, exhibit their real state; and, consequently, tend but to display the inferiority of the most finished performance of the ablest artist, when put in competition with the glorious productions of nature. The finest works of the loom and of the needle, if exhibited with the microscope, prove so rude and coarse, that were they to appear thus to the naked eye, so far from affording delight to our belles, would be rejected with disgust. But the more we inquire into the works of nature, the more fully are we satisfied of their divine origin: in a flower, for instance, we see how fibres too minute for the unassisted sight are composed of others stillmore minute, till the primordial threads or first principles are utterly indiscernible; whilst the whole substance presents a celestial radiance in its colouring, with a richness so superior to silver or gold, as if it were intended for the cloathing of an angel, and we have the highest authority for asserting, that the greatest monarch of the East in all his glory, was not arrayed like one of these. A very few specimens of art will, therefore, suffice.

An inspection of a few of the above articles only will clearly demonstrate, that as in the moral and political world, so in the works of art, perfection is unattainable by mortal man. With the fullest impression of which truth in the mind of the editor, and an appeal to the candour of his readers towards those imperfections which they may have discovered in this performance, he shall now conclude with,

FINIS.

The following is a new, useful, and ready method of making globules for microscopes, differing from the customary one described inpage 8, and is extracted from Mr. W. Nicholson’s scientifical Journal of Natural Philosophy, Chemistry, and the Arts. No. 3, June 1, 1797. p. 134.

“The usual method has been to draw out a fine thread of the soft white glass called crystal, and to convert the extremity of this into a spherule by melting it at the flame of a candle. But this glass contains lead, which is disposed to become opake by partial reduction, unless the management be very carefully attended to. I find that the hard glass used for windows seldom fails to afford excellent spherules. This glass is of a clear bright green colour when seen edgeways. A thin piece was cut from the edge of a pane of glass less than one-tenth of an inch broad. This was held perpendicularly by the upper end, and the flame of a candle was directed upon it by the blow-pipe at the distance of about an inch from the lower end. The glass became soft, and the lower piece descended by its own weight to the distance of about two feet, where it remained suspended by a thin thread of glass about one five-hundredth of an inch in diameter. A part of this thread was applied endways to the lower blue part of the flame of the candle without the use of the blow-pipe. The extremity immediately became white-hot, and formed a globule. The glass was then gradually and regularly thrust towards the flame, but never into it, until the globule was sufficiently large. A number of these were made, and being afterwards examined by viewing their focal images with a deeper magnifier, proved very bright, perfect, and round.”

The opake solar microscope has been made by the late Mr. Martin of larger dimensions than described inpage 106. The illuminating lens, at A B,Plate V.Fig. 1, and the breadth of the mirror were about four inches and an half, instead of three inches, which gives more than double the light of the former; and, consequently, all the larger sort of opake and transparent objects, to the size of one and an half or two inches in diameter, as well as diverting objects painted on glass, like the magic lanthorn sliders, are shewn with the greatest distinctness, and has by Mr. Martin been called theMEGALASCOPEof the apparatus.

The same ingenious and learned artist applied a lattice of small squares about one-tenth of an inch, each square made of fine wire, or lines drawn strongly on glass in a circle of one inch in diameter, and placed these in the compound body of a microscope or telescope, in the focus of the glasses next to the eye. And having a copper-plate lattice of squares disposed into a circle, and to any size as may be wanted, the observer or artist may then with great facility make an exact drawing on the paper of the object observed. The same contrivance is applicable to the solar microscope. This he called theGRAPHICAL MICROSCOPE OR PERSPECTIVE.

Page 127, line 24—Any pocket telescope, the drawers of which are made to allow of a further extension than usual, may be used as a compound microscope for examining birds or insects alive, in a garden on the flowers, shrubberies, &c. from a window near to the objects. There are few pocket achromatic telescopes or perspectives, but what will define and magnify objects from about six feet to any distance from the instrument. The magnifying power is inversely as the distance of the object from the telescope, and, consequently variable in an infinite degree; on which account Mr. Martin named it thePOLYDYNAMIC MICROSCOPE.

Magazines of microscopical apparatus, with collections of objects, fitted up to any extent and to order.

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