instrument, which is used not only to focus with, but also to make the requisite allowance for actinic variation. "The negative intended to be reduced is then arranged vertically, with its centre in the axis of the microscopic body, at a distance of from two to four feet from the lower object-glass, and with a convenient screen of card, wood, or thick paper, to cut off any extraneous light that would otherwise pass beyond the limits of the picture. "A small camphine-lamp is employed for the purpose of illuminating the negative, having a good bull's-eye lens as a condenser, so arranged with its flat side next the lamp that the refracted rays shall just fill the whole of a double convex lens of about six inches in diameter, the latter being placed in such a position as to refract the rays of light in a parallel direction upon the negative. By this arrangement the bull's-eye lens of about two inches and a half in diameter appears as the source of the light instead of the small flame of the lamp. "By using a bat's-wing gas-burner of a good size, a single lens, instead of the two, may be so placed as to give the necessary uniformity of illumination." This arrangement requires the same care in working as that before mentioned, the pictures being produced, developed, and fixed by the same treatment. As before stated, almost every manipulator makes some small changes in the method of producing these minute pictures; but the rules given, though far from new, are sufficient for all purposes; and I may state with truth, that those which I procured when these wonders were quite new, are fully equal in every respect to the best usually met with at the present time. With these instructions I shall close my Handbook, as I believe that every branch of Preparation and Mounting of Microscopic Objects has been treated of. Not that the beginner can expect that he has nothing to do except read this to be able to mount everything; but there are difficulties from which he may be freed by instruction, when otherwise he would have been compelled to learn by failure alone. I may, here, however, repeat certain advice before given, that, when practicable, it is a good thing to mount each object by two or more different methods, as very frequently one feature is best shown dry, another in liquid, and a third in balsam. Secondly, let the mounting be studied thoroughly, as no part of the microscopic science is more worthy of thought than this. And lastly, let no failures prevent you following up what will assuredly one day become a source of great pleasure, and render your daily "constitutional walk," which is often dull in the extreme, very delightful, as it will afford you some new wonder in every hedge-row. INDEX. AIR-BUBBLES, 56. Air-pump, 13; use of, 57. Alcock, Dr., on tongues of Mol- Algæ, mounting of, 91. Anacharis alsinastrum, rotation Apparatus required in mounting Arteries, how to distinguish, in Asparagus, spiral vessels of, 114. as cement and varnish, 18. BAT, circulation of blood in wings Beale's, Dr., Prussian blue for in- Bermuda earth, 40. Bichromate of lead, injection with, Bird, Dr. Golding, on preparation Brass plate for heating glasses, CACTACEE, raphides of, 52. Carmine injecting fluid, Dr. Chalk, foraminifera from, 63. Circulation of blood, 140-142; of Cleanliness in microscopic work, | Elastic objects, to keep flat upon 1. Coal, sections of, 99. Collection of diatoms, 29. Cover of objects, to remove, 60. the slide, 11. Equisetaceæ, 80; spores of, 146. FEATHERS, 73. Feet of insects, 54, 71. Ferns, 51; development of spores Fish, fins and tails of, 50; scales DALE & DAVIES', carmine injec- Fluid, mounting objects in, 83. tion, 138. Desmidiacea, in preservative li- Diachæa elegans, 53. Doyer's, M., method of injection, Dry objects, to mount, 22. Flustra avicularis, 79. Foot of sheep injected, 136. Fossil infusoria, 40. |