44 
PROFESSOR E. RUTHERFORD AXD MR. R„ K. McCLUXG 
tlie cylinder, passed tliroug'li a rectangadar orifice in a thick lead plate. Knowing the 
distance from the source of the rays and the area of the opening, the area of a section 
of the cone f»f rays at any point in the cylinder could be determined. 
The results calculated in this way vrere compared v.uth tlie area of the impression 
on a })h()togra 2 ohic ])late at different distances from the orifice, and it was found that 
file correction to a])]ily for the source of the rays, not being a point source, was 
] )ractically negligible. 
Let l^ he the intensity of the rays at the beginning of the plate 0, and S the area 
of tlie cross-section of the cone of rays at that point. Tlie energy crossing the surface 
per second is TS. 
If there vras no ahsorjition of energy in the gas, the energy crossing the cross-section 
of the cone of rays at the further end of the plate C would he the same as at the 
heginning. But in conseipience of absorption the energy cro.ssing the surface per 
second is 
where I = length of the plate Cl, and X = the coefficient of absorj^tion of the rays in 
the gas. The energy absorbed in the gas jier second is equal to 
LS(1 - = LS\/ 
if \J is small, as was the case in the experiments. 
The current between the jilates A and 0 was determined for a voltage sufficient to 
move all the ions to tlie electrodes before any appreciable recombination could take 
]ilace. 
Let n — total number of ions produced ]ier second. 
I — current between the plates through the gas. 
e = charge on an ion. 
W = average energy requii-ed to produce an ion. 
Then Wr; — LSX/ and i — ??e; 
i 
The value of L was determinefl from the heating effect of the rays, as explained in 
the earlier part of the paper. 
Let = intensity of the rays at tlie surface of the bolometer. 
Pj z= transmission ratio of the rays when passing through the platinum grid. 
Then 
energy absorbed in the grid per second = — P\) > 
where A = area of grid. 
Assuming the value of the intensity uniform over the surface of the grid, and equal 
to the value at the centre, the total energc absorbed in the grid is slightly less than 
