1882.] 



MICROSCOPICAL JOUKNAL. 



185 



dition of the sun and stars, the nebu- 

 lae and comets. We can readily un- 

 derstand 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 tem- 

 perature, the pressures at their sur- 

 faces, the distribution of the elements 

 about their centres, in fact, we are en- 

 abled to study them from a distance 

 of millions of miles with the same cer- 

 tainty 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 de- 

 velopment 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 some- 

 what different construction from the 

 larger instrument. In this instru- 

 ment only a small spectrum is neces- 

 sary, but the definition must be 

 good — the faintest absorption of 

 light should be noticeable in any 

 part of the spectrum. The instru- 

 ment 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 iV, which is illu- 

 minated by the mirror O. The image 

 of the scale is reflected from the up- 

 per 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 microspec- 

 troscope is shown in fig. 41. D is 

 the supplementary stage, and C and 

 H are the screws for ad^sting the 

 slit. The tube A contains the prisms, 

 and ^ 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. An- 

 other 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 im- 

 prove the definition. A cylindrical 

 lens collects the light from the slit. A 

 micrometer is also provided to indi- 

 cate wave-lengths. This miniature 

 microspectroscope is made in Eng- 

 land, 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, mani- 

 festing their presence by dark bands 

 in constant positions. It is well 



