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light, the image wants it; if distinctness or field are wanted, the image is likewise defective in these points. Another very great reformation is cutting short the amplification of the image down to the standard of the magnifying power of the microscope producing it. Thus if the microscope magnifies 60 times, the image is only allowed to be magnified 60 times, and so on: this is done by only suffering the rays to diverge to the distance of six inches. By these means, the maximum of sharpness and distinctness is obtained, so that the image is like a miniature picture, where every thing is seen just as if one were looking through the glasses. What purpose does it serve (save that of astonishing women and children) to suffer the rays to diverge till you have made a flea as big as a jack-ass, &c.
Monstrum horrendum, informe, ingens, cui lumen ademptum-, at the expense too of all light, distinctness, and every thing valuable in vision. My instrument shows none of these wonderful wonders. I hold them in supreme contempt, but in real magnifying power it is nevertheless greatly superior.* No sensible optician ever forces a telescope, or microscope, to a higher power than it is capable of bearing, as the object is not only seen no better (though larger), but a vast deal worse.
If it is asked why I did not, at least, suffer the rays to diverge to eight inches instead of six, eight inches being the standard of sight, I answer, I do not believe eight inches to be the standard of sight, but that it is much less than that. I am not conscious that I am either long or short sighted. I can see to read moderately sized print at the distance of five feet, and I can read the same 44 inches from my eye. When I go to look narrowly into any thing, I generally look at it 4} inches distance. Let any lady, with acknowledged good eyes, take a microscopical object, such as a transparent slider, or some such thing, and let her mark the distance she places it from her eye, when she sees it to the best advantage, so as to see most into its nature. I am sure 99 out of 100 will place it nearer than eight inches. However, I have assumed six inches.
As an opaque solar microscope, this instrument possesses the same advantages over the common one as the transparent part does ; it does not, however, magnify above 60 diameters (common computation), and would, in my opinion, be of no use if it did. I may mention that the common transparent body will not form an image of an opaque body, from its affording so little light.
As a lucernal microscope, this is likewise superior to the common one, for which all that is necessary is to place a fountain lamp on the floor, on one side of the instrument, on the same level with the great mirror, and about two feet distant from it, so that the light may meet the long axis of the ellipse at a right angle ; then every thing goes on as before ; and I think the transparent part of the instrument especially is never seen to more advantage than in this way. The vision altogether is very superior to that of the common lucernal, which is always full of colour, very indistinct, and distorted at the edges of the field. Our instrument will not, however, produce any image in the camera by lamp light—at least, it is a mere sħadow. I have tried every possible kind of microscope, simple and compound, to endeavour to get a decent image by lamp light, but have been totally unsuccessful; the reason of which seems to be this : If you allow the apertures of the lenses sufficient diameter to give å requisite quantity of light, the image is quite confused, and full of colour; if you reduce them to the proper standard, the lamp will not afford light to show it, and here the matter rests. Incidit in Scyllam, &c. The utmost which can be done is to produce an image of a transparent object (an opaque one is out of the question), of which you are enabled to see the outline and something of the colour very slightly magnified ; but into the texture and minutiæ of which, you can see nothing. Of this description is the image of a common lucernal; and, in my opinion, it is not worth looking at. The only remedy for this which occurs to me, would be a lamp which should give as much light close to the instrument as the sun does at his natural distance.
* The real power of the glasses producing the image is about four times greater than that of the lenses generally used for solar microscopes.
The best way to procure an image by lamp light in our microscope is to take the opaque body at its lowest power to view a transparent object (as this body gives much more light than the other), then to get a high stool and place it upon the table with the lamp opposite the large mirror, and proceed as with the sun. The camera must be quite dark. An image will be formed so that any body may affirm the instrument produces an image by candle light; but this is all that can be said of it.
It would not be amiss in packing the microscope to keep the opaque apparatus distinct from the transparent, so that a person inexperienced in microscopes might more readily learn to manage it: from the variety of purposes to which it is subservient, it is somewhat more complicated in its construction than microscopes usually are.
I have neglected to describe a kind of slider which I use in my microscope; it is composed of a glass tube, flattened, and drawn out to the size of a common slider, and polished on one side: its use is to hold microscopical objects which will not keep in a dry state, such as pieces of finely injected membrane, petals of flowers, and the like; these little preparations are introduced into the slider, which is then filled with spirits, ar covered at the end with a bit of bladder secured by a wax thread.
I now proceed to fig. 3, which is a compound microscope, which
would be very useful for dissecting insects, as it shows the image erect like a single lens; its power is about 60 (common computation), nor will it magnify above that with distinctness ; it is composed of seven lenses, and, nevertheless, shows the object very clear and distinct; its body is 102 inches long; it is in its principle the eye-piece of a small telescope, connected with the field and double eye-glass of the common compound microscope; the little eye-piece at the bottom is 39 inches long; as I have it, a body of this nature is made to screw into the arm of the instrument like the other ; but in this state it is not sufficiently steady to be used with comfort, as a very slight tremor is perceptible when you are working. I recommend a stand for it, such as that in fig. 3, made very solid, with a rack and pinion tó move the body like that in Culpepper's microscope.
The advantages of this instrument would be that, being to be used for a continuance, it would not strain the eye like a single lens of the same magnifying power, which would need to be th of an inch focus ; that there would be abundance of room to manage the dissecting instruments, as the focal distance of this microscope from the object is half an inch; and that the operator would not be under the necessity of putting his nose close down over the object, and thereby darkening it, so that the light would require to be thrown up from below and reflected back upon the object by a silver cup.
I do not see any particular utility in this last instrument, except as a dissecting microscope. I have now given a plain account of this instrument without any reference to theory, or any display of algebra and mathematics. I have written for the practical man only, to whom I recommend the instrument as a valuable article of his trade, the cost of which will not exceed that of a good compound microscope of the common make, with a transparent and opaque solar apparatus, and will, I think, give much more satisfaction; at least, to those who can distinguish a bright, clear, achromatic, distinct image, from a distorted, dull, confused one, and who prefer in a solar microscope an image abundantly magnified, and as sharp as a miniature picture, to a huge, indistinct shadow. It is the established practice of every inventor to extol the merit of his own production, and to decry all others; but I do not think I have asserted any thing here of mine which will not bear the closest examination by those most skilled in optical instruments.
Notice of some Animals from the Arctic Regions.
By Dr. Leach.
(To Dr. Thomson.) MY DEAR SIR, In compliance with your wishes, I now transmit to you a hasty list of the mammalia and birds that have been received from the Northern Expeditions, and which have since been sent to the British Museum by the Admiralty. I remain, yours faithfully,
W. E. LEACH,
1. Ursus Albus, Brisson, Jonston (White, or Polar Bear).– A very large specimen, nearly nine feet in length, was brought home by Capt. Ross. It was skinned and prepared by Mr. Beverly, who devoted much time and attention to its preservation.
2. Canis.-A variety approaching to the wolf in many points of external character and in voice. It wants the thumb on the hinder feet.
Baffin's Bay, Capt. Ross. 3. Vulpes Lagopus (Arctic Fox). This animal was received alive, and did not emit the disagreeable odour of the common fox in a great degree: this has been observed before. Coast of Spitzbergen, Capt. Buchan.
4. Phoca Fætida ? Müller, Young (Jacob's bite), June 30, Capt. Ross.
5. Trichechus Rosmarus (Walrus). The head only was received, from Capt. Ross. 6. Lepus
?-Certainly distinct from our White Hare (Lepus albus, Brisson), which again seems to be distinct from the variabilis of Pallas.
It is of the size of the common hare, and of a white colour. The back and top of the head are sprinkled with blackish-brown (nigricante-fusco) hair, banded with white; the sides of the neck are covered with hair of the same colour interspersed with white. The extreme tips of the ears are tipped with black, intermixed with white. The insides of the ears have a few black hairs mingled with the white. As the skeleton was not brought home, it will be impossible to clear up much respecting the three whitecoloured hares above-mentioned. It was killed on Sept. 1, in lat. 73°, on the west side of Baffin's Bay.
7. Cervus Tarandus (Rein Deer). Coast of Spitzbergen, Capt. Buchan.-The heads only of this animal were received. The horns in the growing state are covered with woolly down, much longer in proportion than that on those of the various deer that are domesticated in this country.
1. Falco Smirillus (Merlin Falcon). Lat. 65°, Capt. Ross.
2. Vitiflora Ænante (White-rumped Wheatear).- Killed at sea, by W. E. Parry, Esq.; lat. 59° 51' N.; long. 11° 21' W May 6.
3. Emberiza Nivalis (Snow Bunting).-Capt. Ross.
4. Hæmatopus Ostralegus (Common Oyster-catcher). Ferroe. F. Franks, Esq;
5. Pelidna Alpina (Common Dunlin). 6. Tringa Islandica. 7. Lobipes Hyperboreus, Cuvier (Red Lobefoot), commonly placed in the genus Phalaropus.
8. Rallus Sericeus (Common Rail).
9. Uria Francsii (Franks's Guilemot).—This is a new species of which I have given a description to the Linnean Society. It was first killed off Ferroe, by F. Franks, Esq. who sent it to me; it has since been received from all the ships employed in the northern expedition.
10. Grylle Scapularis (White-winged Scraber).—All the ships met with this bird. It is commonly denominated Black Guilemot, but has been referred to a distinct genus, named Cephus by Cuvier; a name which I cannot, for many reasons, adopt.
11. Mergulus Malanoleucos (Common Sea-Dove).-Killed by all the ships.
12. Fratercula Glacialis (Northern Puffin). This new species, on which I have sent a paper to the Linnean Society, was killed off the coast of Spitzbergen
13. Procellaria Glacialis (Fulmar Petrel).-Spitzbergen and Baffin's Bay.
14. Larus Eburneus (Ivory Gull).-Baffin's Bay. 15. Larus Rissa (Kittiwake Gull).-Spitzbergen. 16. Larus Canus (Common Gull.)—Ferroe. F. Franks, Esq.
17. Larus ?-A large species not yet determined. Baffin's Bay.
18. Larus ?-Young, of a large species not determined. 19.
A paper on this bird (which forms an intermediate genus between Larus and Sterna) has been read to the Linnean Society, by Joseph Sabine, Esq. who named it Larus Sabini, after his brother who first killed it.*
20. Sterna Hirundo (Common Tern).-Ferroe and Spitzbergen. 21. Stercorarius Cepphus (Arctic Jager).-Baffin's Bay.
22. Catarracta Fusca (Squa Catarractes).-Ferroe. F. Franks, Esq.
23. Somateria Mollissima (Cuthbert's Eider).–Baffin's Bay, Spitzbergen.
A great number of other species were killed by individuals, which have not been deposited in the British Museum.
See Linnæan Society report, p. 67.