14 



DENSITIES Ol" dXVCEN ANH IIYUKOUEN 



The otlier niellioLl useil to olttaiu the st)lici contents of some globes, ct>usisted 

 in determining the specific gravity of the glass of the globe from the part cut off 

 in fusing on its stopcock, from which the solid contents of the globe minns the key 

 of its stopcock could be computed; to which was added the solid contents fif this 

 key. 



9. COMl'HKSSIO.N ()!• <iI,olii:s WHEN EXHAUSTED. 



The volume nf a hollow glol)e varies with the variations of [iressurc t<i which 

 it is subjected. The amount of variation ilue to a given difference of pressure 

 depends ou the radius and on the mean thickness of the walls of the globe, and ou 

 the variations of the thickness on different [)arts of the surface. For the globes 

 used in these experiments, the difference of volume due to the exhaustion of the 

 globe was from one six-thousandth to one twenty-five-hun<lrc(lth of the capacity. 



Fig. 4. — Apparatus for mcisiiring comprcNsion of glol)(.s on exhaustion. 



This change of volume must be detenniued with accuracy. A convenient 

 method was employed. A copper cylinder, 1 1, Fig. 4, Iia<l a cover //^ which could 

 be soldered to the cylinder and easily removed again. In this the globe a was 

 placed ; sometimes it was nearly filled with water, sometimes it was held down by a 

 sinker. The globe was connected by a thick ridjber tube to the glass tube r leading to 

 a syphon gJiiige and to an air-pump, and the cylinder was ueaily tilled with water. 



