ox ENERGY OF RONTGEX AND RECQUEREL RAYS, ETC. 
45 
the above amount, and it has been shown earlier in the paper that very approximately 
the energy absorbed in the grid = 'OSI^A (1 — p,). 
In practice the current in the discliarge cvlinder was o])served at the same time 
as tlie heating effect. Tlie cylinder was placed l)ehind the platinum giid in such 
a position that the ravs entering tlie cvlinder jiassed slightly to one side of the 
centre of tlie grid, thus avoiding the mica frame of the bolometer. The luys before 
entering the cvlinder were cut down in intensitv bv their passage tlirough the grid, 
by the enclosing envelope and the aluminium window in tlie discharge cvlinder. 
Let p., = transmission ratio of the rays through the })latinum grid + Hi*? f*?lf 
cover + the aluminium windov', &c. 
= distance of grid from source of rays. 
Let fL = distance of the beginning of the plate 0 in the discharge cylinder from 
the source of the rays. 
Then it can easily be seen that 
I, 
b 
- P: JJ e 
(!)• 
’I’he factor e is nearly equal to unitv, and is tlie correction for the absorption 
of the ravs in the gas between the grid and the discharge cylinder. 
If H is the number of heat units communicated to the liolometer per second, tlien 
and 
•98AL(1 - pi) = JH 
_ LSX/e 
Dividing (3) by (2) and substituting the value of L b ffom (1), we obtain 
411 
•OSAA - p) 
S\/e 
i 
■ Pi 
1 - 
A- 
Determination of i. 
The value of i Avas determined by an electrometer with an additional capacity of 
•00248 of a microfarad in parallel. Tlie heating effect on the bolometer and the 
quantity of electricity discharged between the plates of the cylinder were obseived at 
the same time. A lead screen cut off the rays from the platinum grid and the 
discharge cvlinder for 15 seconds after the bulb had started, for it Avas found that the 
rays gradually increased in intensity for the first 10 or 15 seconds. At the end of 
15 seconds the lead screen Avas suddenly remoA’ed by a cord operated from a distance. 
After the passage of the rays for 30 or 45 seconds, the rays AA-ere stopped. The 
deflection from the zero of the bolometer AA-as taken by one obser\’er, AAdiile the 
