sis may be readily illustrated by a few simple experiments. We have here the colorless flame of a Bunsen burner. I take a platinum wire with some common salt upon the end This FIG. 40. SLIT OF ZEISS SPECTRAL-OCULAR. colors the flame yellow. Examined. with a spectroscope we find only a single yellow line indicating the presence of sodium. Strontium and lime The it their characteristic colors. spectroscopic examination of these flames shows that the lines produced by each element occupy different positions in the spectrum, so that by measuring the places of the lines in the spectrum one can readily determine the composition of the flame that produces them. Most metals, however, require the more intense heat of the electric arc to develop their characteristic lines, and a few elements, as carbon and boron for example, are only volatilized in the intense heat of the sun. The temptation to dwell upon the applications of the spectroscope in solar and stellar physics is great, for this subject is, to me, one of the greatest interest. I would be pleased to review the progress of this branch of investigation during the past twenty years. In no department of physical research have important discoveries followed in such rapid succession; in no department have results of such FOLLINGS. FIG. 41. SORBY-BROWNING MICROSPECTROCOPE. give a red flame, baryum a green, potassium a violet, and several other metals are sufficiently volatile at the temperature of the flame to impart to a surprising character been so readily revealed. I would be glad to speak at some length of the recent researches upon the chemical and physical con dition of the sun and stars, the nebulæ and comets. We can readily understand that the spectroscope may reveal the composition of these distant suns and masses of fiery vapor, but it has told us much more than that; it has enabled us to measure their rate of movement toward us or from us, it has afforded a measure of their temperature, the pressures at their surfaces, the distribution of the elements about their centres, in fact, we are enabled to study them from a distance of millions of miles with the same certainty of our results, as when we test a mineral in our laboratories. Every ray of light which comes to us from the depths of infinite space, though it may have travelled years and years before it reached our world, bears the impress of the physical and chemical conditions of the sphere from whence it came. It is the labor of the scientific student to interpret its silent testimony. As we go out beneath the starlit sky, and think that every ray of light from every shining world brings us a story like this, a history of the birth and development of worlds, or systems of worlds, or nebulous stars-perhaps we may realize what the spectroscope has already done for chemistry and physics. The microspectroscope is of somewhat different construction from the larger instrument. In this instrument only a small spectrum is necessary, but the definition must be good the faintest absorption of light should be noticeable in any part of the spectrum. The instrument I have to show you this evening is a spectral-ocular by Zeiss (figs. 39 and 40). Fig. 39 represents a sectional view of the instrument. It will be seen that the lower part is an ordinary eye-piece with its two lenses, but in place of the ordinary diaphragm there is a slit, adjustable in length and breadth, shown in fig. 40. By studying this figure the method of adjustment, with two screws, F and H, and the projecting lever which carries a reflecting prism, can be readily understood. The upper part of the instrument swings about the pivot K, so that by opening the slit the eye-piece can be used for focussing an object, the slit being the diaphragm. The upper portion contains the prisms, and also a scale in the tube N, which is illuminated by the mirror O. The image of the scale is reflected from the upper surface of the last prism to the eye, and when properly adjusted gives the wave-length of the light in any part of the spectrum. There is also a supplementary stage, not shown in the figure, upon which a specimen can be placed, and its light thrown up through the slit by reflection from the prism on the lever shown in fig. 40, along side of the light from the object on the stage of the microscope, thus enabling the spectra from the two sources to be directly compared. The Sorby-Browning microspectroscope is shown in fig. 41. D is the supplementary stage, and C and H are the screws for adjusting the slit. The tube A contains the prisms, and B is a screw for focussing the spectrum. There is no scale of wave-lengths with this instrument, but there have been several methods of mapping the spectra devised, which can be readily applied. Another form of microspectroscope has been devised by Mr. Sorby in which the object glass that focusses the slit is above the prism instead of below it. This arrangement is said to improve the definition. A cylindrical lens collects the light from the slit. A micrometer is also provided to indicate wave-lengths. This miniature microspectroscope is made in England, by Mr. Hilger. The application of the spectroscope to the examination of solutions or fluid compounds, is based upon the discovery that some coloring matters exercise a selective absorption upon certain colors in the spectrum, manifesting their presence by dark bands in constant positions. It is well known that the color of a transparent object is due to the absorption of certain colors from the light-thus, a red glass permits the red rays of the spectrum to pass through it while it is opaque to all the others. Hence, if we examine with the spectroscope the light from such a glass we find that the spectrum consists only of a band of red, all the other colors being absent. Such a spectrum might be given by a large number of totally different substances of a red color, since there is no distinguishing characteristic of a spectrum formed by a general absorption of this kind. But there are many colored solutions and compounds that exercise a selective absorption upon the light that enters them, that is to say, when the transmitted light is analyzed by the prism it shows, not a single band of color as in the former case, but a continuous spectrum with one or more dark bands crossing it, indicating what colors have been absorbed. The position of these bands is constant for the same compound; hence, we have a means of detecting certain compounds, and analyzing mixtures of them, by the character of the light they transmit. Take, as an example, the coloring matter of blood, the spectrum of which will be shown this evening. There are two distinct, dark bands in this spectrum which always Occupy the same position. As an illustration of the ease with which two coloring matters may be distinguished in a solution, we may allude to the experiments of Mr. P. Petit in studying the coloring matter of diatoms. It has long been known that when certain species of diatoms are dried, the brownish, or yellowish, endochrome changes to a bright-green -such a change is particularly noticeable in Melosira, and in the beautiful Aulacodiscus Kittonii, of which I have an excellent collection illustrating this fact, and doubtless it is true of many other species. An examination of the spectrum of the coloring matter of diatoms known as "diatomine," has afforded an explanation of the change of color, and has shown that diatomine is a mixture of the two coloring matters which are common throughout the vegetable kingdom, phycoxanthine and chlorophyll-the former is yellow, the latter green. It is clearly shown by Mr. Sorby's investigations on the coloring matters of plants, described in the Proceedings of the Royal Society, 1873, P. 442, that each of the above-named coloring matters, as distinguished in diatoms by Mr. Petit, is composed of several distinct coloring matters, but to illustrate the application of the microspectroscope to analysis of this kind, we may assume the correctness of the distinction recognized by Mr. Petit. According to his experiments, the different colors of diatoms are due to the different relative proportions of these two constituents. For example, Melosira and Navicula contain a larger proportion of the green than Nitzschia or Diatoma. This is clearly shown by the spectra, which are represented on the board. The first spectrum represents the absorption due to chlorophyll, the second is that of phycoxanthine. Observe the difference in the position of the dark bands in the two spectra; in the latter the bands is further to the left. sence The third spectrum represents the coloring matter of Melosira nummuloides. The three fainter bands of chlorophyll are present, and the broad, black band indicates the preof both phycoxanthine and chlorophyll. In the fourth figure there is not a sufficient quantity of the chlorophyll present to develop all of the faint bands characteristic of that substance, but that some is present is shown by the broad band on the left, which also shows the presence of phycoxanthine. By the aid of the spectroscope and chemical analysis, Mr. H. C. Sorby, in the article already referred to, has shown the presence of twelve distinct colors in the red, olive, and green algæ. The examination of blood with the microspectroscope is of great importance in legal proceedings. To Prof. Stokes we are indebted for some very elaborate investigations of the coloring matter of blood. His results were published in the Proceedings of the Royal Society, 1864. He found that when blood was treated with some reducing agent, such as a solution of ferrous sulphate containing tartaric acid, or stannous chloride, the color was changed from a bright scarlet to a purple. This change in color is accompanied by a modification of the spectrum, the two bands characteristic of oxygenated blood being replaced by a single band occupying a position between the places which they held. He named bright-red constituent scarlet cruorine, and the other purple cruorine. When the reduced or deoxydized blood is shaken up with air the scarlet cruorine is again formed, and shows the two-band spectrum as before. These changes are quite characteristic of blood, but there are still others, brought about by acting upon blood with acid and alcohol, which render spectroscopic examination still more conclusive of the nature of the fluid under examination. the The delicacy of the test for blood by the microspectroscope is quite remarkable. A scarcely visible stain upon a piece of white paper, not more than 1000 of a grain, will show the bands, but it is more satisfactory to work with solutions of blood. A quantity not greater than of a grain of blood in a cell measuring of an inch in diameter by half an inch deep will show the bands very clearly. A New Form of Constant Pressure Injection Apparatus.* BY PROF. WILLIAM LIBBEY, JR. In studying the circulatory system, the means of injection are an indis *Read before the Section of Histology and Microscopy of the A. A. A. S., at Montreal. pensable aid. This operation can be performed in several different ways, but the most satisfactory method would, of course, be that which would in the simplest manner utilize the materials used, and at the same time place them under the most perfect control of the operator. In the piece of apparatus described below, the wants of my laboratory have been especially consulted, and the object kept in view was the construction of a machine which would perform the most delicate injections in a satisfactory manner. In a sense, it may be said that this object has been realized; but, as the element of good judgment can never be made part of a machine, the degree of success will still be in proportion to the skill in manipulation. All such machines must have a certain similarity in their construction, but may differ essentially in the arrangement of their several parts, and for this reason no great originality is claimed for the apparatus; the method of the operation in the machine under consideration is as follows: We will suppose the animal, or organ, to be injected to have been prepared as is usual, and placed over a water-bath arranged to secure a proper degree of temperature during the operation; the injectionmass having been also previously prepared and placed in a threemouthed Woulffs-bottle (prepared as a wash-bottle with closely-fitting rubber corks), which should, of course, be placed over a water-bath to keep the mass liquid. The source of the power utilized is twenty pounds of mercury, which, by changing position from a higher to a lower level, forces the air out of one of two globular glass filtering funnels. alternately, as one is placed below or raised above the level of the other, which should be kept stationary. These two filtering funnels are supported on iron rings with clamps which can be attached to two iron rods at any given height. The iron rods should be about 36 inches high, being held in their places by a framework that rises on the back part of a wooden platform which rests upon the table (or may be built into the wall, or placed between two shelves far enough apart in a closet in the laboratory), and serves as a convenient place for any accessory apparatus or instruments. The funnels referred to above, are connected at the bottom of each by a rubber tube, and have stopcocks above the points where the tubing is attached. The opening at the upper part of these funnels is closed with rubber corks, through which a glass tube is placed after having been once bent at right. angles. The means of securing the operation of the currents of air, in such a manner as to perform their work of which it forms a part has been connected with the glass tube at the top of the filtering funnel, from which the air is forced by the flow of the mercury to it from the other funnel, which should occupy a higher position. It also affords the means of allowing a current of air to flow to the surface of the mercury in the higher vessel, through the other stopcock which should be turned so as to afford ingress to the air; this will be secured when the stop-cock is placed FIG. 42. CONSTANT PRESSURE INJECTION APPARATUS. properly, is an arrangement of threeway stop-cocks of a peculiar construction. These stop-cocks are each so constructed that when turned in one position they have the form of a regular spigot, while, by a quarter turn from that position, a straight connection is made through the body of the stop-cock to a tube opening at that point. Two of these stop-cocks are placed, one on each of the upward branches of a glass tube having the form of the the letter Y. This arrangement affords the means of transmitting a current of air under pressure through that stop-cock which may be turned so as to open a straight connection through it, when that branch of the Y in a position at right angles to that of the first described stop-cock. This branch of the Y-tube should be connected with the tube at the top of the other filtering funnel. The lower branch of the Y-tube should be connected with the short arm of the bottle containing the injection mass. All the joints made with the tubing should be securely wired, and all the other connections made as tight as possible. The Y-tube described above should be securely supported by extension test-tube clamps, attached to the iron rod to which the stationary filtering funnel has been fixed, and below the funnel. The long arm of the bottle con |