ZOOLOGY AND BOTANY, MICBOSCOPY, ETC. 



539 



Interferometer.— This instrument (fig. G2) was shown at] the June 

 Meeting and was described fully by C. Beck (see Proceedings, p. 565, of 

 the present number). 



Fig. 62. 



Micro-spectroscopic Observation.* — F. J. Keeley points out that 

 while rnicro-spectroscopy has been largely used with transmitted light, 

 very little application of it has been made with reflected light. Yet 

 with reflected light it is not only suitable for use with small quantities, 

 but has a number of additional advantages. Thus he finds that absorp- 

 tion bands are usually more distinct ; a small crystal on a mineral 

 specimen or a gem embedded in an opaque setting may be examined 

 without disturbing or damaging it ; and phenomena such as iridescence 

 on opaque substances may be studied. 



The Microscope used for this purpose should always be a binocular, 

 which permits the object to be examined through one tube, while the 

 spectroscopic ocular is applied to the other. The illumination should 

 preferably be rather brighter and whiter than is generally necessary for 

 the examination of opaque objects, and is best concentrated by means of 

 a parabolic silvered reflector attached to the objective. For preliminary 

 examination, the older form of micro-spectroscope, as made by Browning 

 or Beck, is preferable, as very faint bands are more readily noted in its 

 short, bright spectrum ; but for further study and for recording the 

 spectra, the Zeiss model with photographed scale is more desirable. 



There are two classes of spectra which can be advantageously studied 



* Proc. Acad. Nat. Sci. Philadelphia (Feb. l'Jll) pp. 106-16. 



