1889.] © Alternating Currents and on the Telephone. 325 
were surrounded by a conductor at zero potential at a distance 
4 metres from it, or that c is of the order 1/15; this is a small 
estimate for c, but the effect of any change is easily calculated 
as the distance the vibration travels before falling to 1/e of its 
value is in Cases IJ. and III. inversely proportional to c, and in 
Cases II. and IV. to the square root of ¢. 
The specific resistance of copper is taken as 1600, that of iron 
10*, and pw for iron 500. 
Briere ot| ianetee of chee ander |Diaeoey elects 
which the Wire in centi- | which 1t | vibrations travel before falling 
wire is made. | metres. falls. to 1/e of their original value. 
Copper “4. ig! 1500-—1500 | 
Iron “4D nV 150—60 
Copper “2 II 400—400 
Tron 2 | Vi 100—40 | 
Copper al I 160—80 
Tron all I 64232, 
Copper 02 I 32—16 
Tron ‘02 | I 16—6 
(2) On the Effect of Pressure and Temperature on the Electric 
Strength of Gases. By J. J. THomson, M.A., F.R.S., Cavendish 
Professor of Experimental Physics, Cambridge. 
THE following experiments were undertaken to investigate the 
changes which take place in the electric strength of a condensible 
gas when the pressure is increased beyond the point necessary to 
liquefy it. 
The gas chosen was carbonic acid, and the electric strength 
was tested in the following way. 
CDF is an iron rod with a cylindrical cavity bored in it, into 
the top of this a glass tube AB with very thick walls is fastened 
with sealing wax, and into the bottom of it an iron screw H GF’ H 
with a hole GH running up the middle of it is screwed. HKLF 
is another iron tube filled with mercury and containing a screw 
NM which can be screwed up and down, this is screwed on to 
the piece L’GF H. A manometer gauge PQ is let into HCDF 
and indicates the pressure of the gas in that vessel. 
The glass tube Ad is initially open at both ends, and CO, 
is allowed to run into HCDF through the glass tube and out 
at H for 6 or 7 hours. The end A is then fused up, and the 
hole at H closed with a small piece of paper. This portion of 
