Chemistry and Physics. 465 
but allowing the apparatus to rest for some hours or days brought 
it back. Inserting a wire which had never before been subjected to 
a current, drove the needle wildly to one side, although its resist- 
ance was but ‘1 of a unit. Suppose the circuit produces no deflec- 
tion, and a wire is introduced which deviates the needle; make 
remove the wire, when the deflection will reappear. If again 
made to disappear and the wire once more inserted, it will now 
@ wire terminating in a sphere and separated from another wire by 
a thin layer of air, would therefore show unilateral conductivity, 
the current passing in one direction more easily than in the other, 
Metals condense gases in great quantity at their surfaces, and it is 
quite conceivable that if two wires are screwed together, that par- 
ticles of air will separate the two surfaces and that a small voltaic 
are will be the result.— PAil. Mag., x|viii, 251. E. 0..P 
} Gases.—W1EDEMANN has succeeded in 
pelled from the bag by admitting water from the reservoir. 
20 litres cooling from 100° to 20° raised the temperature 8°. To 
produce the same elevation Regnault required 200 litres, a serious 
