tive I have seen. The mechanical work is very good, the appearance neat, and the lenses, when tested on the artificial star, appear to be very well centered and figured, and the coma is inward and not excessive. So far as could be judged from outside appearances, for I made no attempt to unravel its mysteries of structure, it is what is now called a "threesystem" objective, though M. Zeiss in his circular mentions it as a "four-system"; the front lens is, apparently, too large for any "four-system" construction of equivalent focus. Considering the inexpensive character of the mounting, compared with the elaborate and nice workmanship required for the mounting of a first class th or 6th, this objective is put at an exceedingly high price-240 thalers in Jena, say 60 dollars gold, to which must be added duties, etc., if imported in the regular way. It ought to do superior work. The balsam angle of this objective, i. e. the angle of the emergent cone in balsam as actually measured, is the same as that of ath Spencer, belonging to a gentleman of this place, which was made at the same time with, and indeed is the same in every respect as the two objectives I had sent to my friends in Europe. With this objective I compared the new Zeiss, and also with a 6th of much larger balsam angle, not yet completed in its own mounting, though finished optically. I beg here to say that I am no partizan either of the Spencers, or of Mr. Tolles; I do not own an objective made by either of them, higher than a 2/3 of 35°. With my friend, who owns the "Zeiss," I believe in the "survival of the fittest." I am only interested in seeing fair play, and I am sure that neither M. Zeiss nor my friend in Germany, who endorsed him so highly, in the comparison with the American objectives, will question my right either to criticize or to publish the result, so long as I state facts which rest not alone on my own testimony, though I may be pardoned for saying I deem that sufficient. The objectives were tried in as precisely similar conditions as possible. The same frustules of Amphipleura, the same light-alternately changing the objectives, with direct (axial) light, and with oblique, by day light and by lamp light. With the mirror alone, and with the "Wenham reflex." And this not once, but a great many times. The tests were both dry, and balsam mounted, Amphipleura, and for the axial light I had a remarkably excellent specimen of the Podura scale. With the day light used in any way, the 6th and theth were manifestly superior to the Zeiss. Fortunately, I am relieved of any charge of improper manipulation, as the "Zeiss "came furnished with oil specially prepared for it, and needed no manipulation. There was nothing to do but change the objective, and make the "oil," which is abominably thin and runs almost like alcohol, stay in, especially with thin covers, and the stage at all approaching the vertical; this feat, however, was successfully accomplished, and I may add, that before applying the oil, the slide was thoroughly cleaned, so that no remnants of the glycerine, or water, used with the other objectives, should interfere; a process also necessary on again changing from the "Zeiss" to the "Spencer." If I knew how to do a fair thing, I am sure it was done at this trial, and I freely confess the result is not what I anticipated. With the Spencer objectives, the outlines of the frustule, and the lines themselves on the valves, were much more sharply defined than with the "Zeiss." There was no difficulty at all, with mirror alone, and ordinary sky light, in resolving the Amphipleura dry, with the "Zeiss," what would have been called superior resolution, if it had not been seen better with the same light, without touching the mirror, with the Spencer objectives. There was a smoky appearance with the "Zeiss" on the dry mount, and an indistinct outline of the valves, with a tendency to break down with the E eye piece, which was entirely absent from the two objectives compared with it. The lines were also seen on Amphipleura in balsam, by day light, but requiring much stronger light to see them best with the "Zeiss," indeed, closer vicinity to the sun than with the "Spencer," the latter exhibited here also the lines considerably sharper. With lamplight and mirror, the results were the same, all the objectives resolved the balsam mounts, but the difference was unmistakably in favor of theth and the 6th. With the Wenham reflex, tried many times on the balsam mounted Amphipleura, the "Zeiss" did its best work, and more nearly equalled theth than it did the %th; but still here, the American objectives not only showed the markings blacker and finer, but stood the test of deepest eye pieces. without flinching, better than the "Zeiss." In all these trials other witnesses were present, and the difference was clearly recognizable-markedly so with ordinary day light and mirror. On Podura, after what I have already said, I need scarcely remark that the same difference was apparent. Indeed, as the same oil is not suitable both for extreme and for central illumination, and I had but that which the owner of the objective sent with it, it is not, perhaps, fair to M. Zeiss to dwell too strongly upon this test. Now, in all I have said, I beg not to be understood as depreciating the Zeiss objective. It is, by far, the best foreign objective I have ever handled. There was a satisfaction in being relieved from any responsibility in adjusting. For my own part, I felt so much satisfaction in this, that I hope the Spencers may be induced to make similar objectives. Finally, it must be remembered, even granting for a moment that my excellent friend in Germany did succeed in resolving test objects much better with the "Zeiss" than with the "Spencer," that the latter was also a very good objective as a dry, and there are hundreds of cases where an oil, which dissolves balsam, and asphalt, etc., cannot well be used; or possibly he may have employed water as the immersion fluid, which is only proper for direct (axial) illumination, instead of glycerin, which is necessary for very oblique illumination THE MICROSCOPICAL EXAMINATION OF FIBERS. BY W. H. SEAMAN. Numerous isolated observations on this subject may be found in works on microscopy, but few attempts have been made to unite these in a connected system.* Many of the statements floating in popular journals are erroneous, and as the determination of the nature of fibres is one of the questions often presented to the microscopist, we offer the result of our experience, A fiber is any flexible filament used in making cordage or woven or felted fabrics. They may be compared with each other as regards their1. Origin, animal or vegetable. 2. Form of section, diameter and length. 3. In animal fibers, color, surface and general shape. 4. In vegetable fibers, diameter and length of ultimate cells. * The best treatise yet published, is "Vetillart sur les fibres végétales employes dans l'industrie.” See also a special report by Hunt & Schaffer, Bulletin Nat. Ass. Wool Growers, 1875. 5. Behaviour with reagents. 6. Relations to polarized light. Animal fibers are either silk, feathers or hair. The smooth, solid, cylindrical form of silk fiber is too well known to require much description. The length is indefinite, and the diameter uniform or nearly so, which is a marked peculiarity. The ends are square, and, as seen in manufactured goods, there are usually particles of stiffening, etc., adherent to the fibers, which in certain forms seem to be regarded by some authors as permanent, and there is entire absence of cell structure. Feathers, either in whole or part, have at different times been employed as fibers. They are usually covered with sharp barbs arranged at uniform distances, and may often be sharply differentiated from cotton, with which they are generally mixed in woven fabrics, by polarized light, in which they are quenched while the cotton glows brilliantly. Feathers, in structure, are modified hairs, and display a somewhat similar arrangement of cells. But most textile fabrics of animal origin are composed of hair, which varies from the rigid spines of the porcupine to the softest and most delicate fur or wool, without changing its type of structure. All hairs are composed of short overlapping scales forming a kind of tube, more or less serrated on the surface, and inclosing one or more rows of medullary cells arranged in symmetrical and characteristic modes, enabling the microscopist to assert with considerable certainty the animal from which they are derived. The shape is usually tapering; often the same animal wears two or more distinct kinds, as the fox, seal, or cashmere goat, coarse long hair forming the outer coat, and fine curly wool the inner. The duck bill (Ornithorhynchus) of Australia, and the common water mole (Scalops aquaticus), have hairs very long, slender, and with the ends flattened out like a trowel.* All fibers of animal origin when burned give a disagreeable odor, and leave a crispy coal, while those of vegetables consume more perfectly without smell. Both silk and wool are soluble in strong hydrochloric acid, the solution being hastened by heat, but in dilute acid silk is soluble and wool is not. Vegetable fibers in the same reagent are disintegrated but not dissolved. * See Micrographic Dictionary for figures of a variety of hairs, feathers, etc. In strong cold sulphuric acid, silk quickly turns yellow and dissolves, cotton disintegrates slowly without color, flax and hemp make a black mixture, and wool is scarcely affected. Both silk and wool turn yellow and are soluble in nitric acid, the first the more speedily, while vegetable fibers are slightly affected. For these, cupro-ammonium sulphate is considered the only solvent. When treated with iodine and dilute sulphuric acid, vegetable fibers, composed chiefly of cellulose, take a characteristic color, either yellow or blue, while animal fibers are not affected. These reagents, applied under the microscope, afford the means, in connection with the characters of the ultimate cells of which all plant fibers are composed, of determining the species from which the fiber is derived. The reagents should be prepared as follows:-Dissolve one part potassium iodide in one hundred parts of distilled water, and add an excess of pure iodine so that the solution shall always remain saturated. Mix one part of distilled water with three parts of sulphuric acid, and when cool add two parts of Price's glycerin. Both reagents should be kept in glass stoppered bottles, and as they are liable to change, should be occasionally tested on known fibers. When in proper condition they will give clear and uniform coloration without changing in the slightest degree the form of the fiber cells. If the acid be too strong the fiber takes an intense color, and swells enormously, often in a very symmetrical manner as figured in Sach's Botany, English Ed., page 592, etc., but this tumefaction should be carefully avoided in differentiating fibers. The simplest form of vegetable fiber consists of appendages to seeds like cotton; single cells almost without taper, but usually they are composed of bundles of tapering or spindle shaped tough, firm cells, lying side by side, and separable from each other by soaking in alkalies, rubbing with the fingers, teasing with needles, rubbing with a pestle, or recourse must sometimes be had to boiling in ten per cent. soda lye or Labarraque solution. When the cells are separated a number of them should be extended on a slip and slightly moistened with glycerin, which will restrain any tendency to crisp or curl when the cover is imposed. By laying the slip on a rule the average length is determined, then a micrometer must be used for the diameter. Now observe the ends for shape, taper, and whether or no |