DISRUPTIVE DISCHARGE OF ELECTRICITY. 643 
where V denotes the difference of potential of the discs, and p the pressure of 
the dielectric; which gives a=102°81 compared with 103°53 for the single 
spark ; and 62=3-6016 compared with 4°8508. The two curves are represented 
together on fig. 13. 
Table X XI. contains an investigation of the same problem with this differ- 
ence, that the length of spark was 1 centimetre, whereas in all the preceding 
series of observations it was ‘5 centimetre. The equation is similar. The 
ratio of the of the ‘5 centimetre curve to that of the 1 centimetre curve ought 
38:878 
70:207 ’ 
give 568. 
I regret that I did not take a series of observations in the reverse order, for 
it may be that the exhausting of the air before taking the observations took 
away the condensed air in great part. The curve for hydrogen instead of air 
(Table X XIT. fig. 6) happened to be investigated in the reverse order. The 
mean points lie very accurately on an hyperbola, excepting that for 262, where 
there may have been an error in reading the number. The equation 
to be that is 554. The mean equation and the equation of this table 
V=012./ {p’ + 600p} 
gives a=300, and J=3:600. The largeness of the a compared with that for 
air affords an additional ground for inferring that the order of procedure is not 
indifferent. 
The Electric Strength of Different Gases. 
Table XXIII.—The first values for air were taken before any exhaustion was 
made; and each of the observed differences of potential, with the exception of 
the second, the smallness of which is probably due to a mistake of 10 in read- 
‘ing, is decidedly greater than any afterwards observed for air. The less value 
of the subsequent readings for air must have been due to the exhaustions 
involved in the change of gas, which were always to 3 mm. or so. It does 
not seem due to any change of sensitiveness in the electrometer; for then there 
would have been a falling off in the third and fourth mean values. Hence 142 
has been chosen, and not 152, as the proper reading for air, and the values 
given in column 6th are deduced from 142. Column 7th contains the mean of 
all other determinations made of the relative electric strength; and these 
means agree pretty closely with the values of column 6th. Column 8th con- 
tains FAaRADAY’s values. (Section 1388 of “Experimental Researches in 
Electricity.”) These numbers all agree in being less than the corresponding 
jnumber in column 6th ; but this is explained by the fact that FARADAY’s num- 
