Chemistry and Physics. 63 
near as possible to the source of heat, when air of ordinary den- 
sity, or even rarefied, surrounded the balance. Whenthe pressure 
was 5 mms., the attraction was still strong, With a pressure of 
uum 
formed so perfect that it would not transmit an electric current, 
when the repulsion was decided and energetic. Projecting ona pith- 
themselves with a variety of substances, as metals, ivory, char- 
coal, ete. 
stellar void. In the radiant molecular energy of cosmical masses 
may at last be found that “agent acting constantly according to 
known laws” which Newton held to be the cause of gravity.— 
Quart. Jour. Sci., xlii, 274. ROP, 
8. Double refraction of a Viscous Fluid in motion.—Professor 
Maxwett, in a paper before the Royal Society, states that a 
viscous fluid, according to Poisson, behaves as an elastic solid 
periodically liquefied for an instant, and solidified again, so that at 
each fresh start, it becomes for an instant like an elastic solid 
ree from strain. The state of strain of certain transparent bodies 
may be investigated by this action on polarized light. This action, 
observed by Brenslet, was shown by Fresenel to be an instance of 
double refraction. : oe 
To ascertain whether the state of strain in a viscous fluid in 
motion could be detected by its action on polarized light, a cylin- 
drical box was made with a glass bottom. In this a solid cylinder 
could be made to rotate, and the fluid to be examined placed in 
the annular space between the cylinder and _the sides of the box. 
Polarized light was thrown up through the fiuid parallel to the axis, 
while the cylinder was made to rotate. No effect was, however, 
obtained with solution of gum or syrup. Canada balsam, which 
had been very thick and almost solid in a bottle, affected the light 
when compressed. 
