on. the use of Carbon bisulphide in Prisms. — 275 
The results which have been given in the preceding pages 
seem to have a two-fold bearing. In the first place they prove 
that by the simple expedient of stirring the liquid in a prism by 
means of a propeller or other device so as to keep it in active 
motion, all strize due to temperature-changes may be prevented 
and the definition rendered perfect. Even carbon bisulphide, 
Whose extreme mobility and high expansion-coefficient make it 
extremely sensitive to variations of temperature, may be made 
i 
trains of glass prisms, and even gratings unless these are of 
large size and are used with telescopes of proportionately large 
apertures, 
i 
perature. Mendenhall calls attention to the effect of this change 
“pon the determination of the position of spectrum lines, espe- 
e 
Gladstone and Dale’s law for carbon bisulphide. When the 
Prism was cooled from 22° C. to 9-6°, the double sodium line 
moved toward the violet end of the spectrum over a distance of 
* Phil. Trans., 1858, 887 
t This 1 : : 
t Ibid. 111. Xv, 269, April, 1878. Hastings calls attention to the new and note- 
