1898-99.] Rev. A. Moffat on Energy of the Bontgen Bays. 437 
cathode from the screen was 6*2 cm. If, then, the screen had 
been at a distance of 1 cm. from the anti-cathode, the intensity of 
the radiation would have been (6*2)' 2 , i.e ., 38*4 times the intensity 
stated above, viz., 38*4 (4 x 10~ 4 ) = 154 x 10~ 4 Hefner lamp. 
If we admit that the whole energy of the Rontgen rays is trans- 
formed into light energy, the intensity of the Rontgen rays would 
be 154x 10 ~ 4 Hefner lamp. Now, the energy of the light emitted 
by the Hefner lamp in one second is 0489 watt. Therefore the 
part of the energy of the Rontgen rays transformed every second 
into luminescence is 0*002911 watt. Now, we have found that 
the luminescence lasts for only yqVo whole time which 
elapses. If, then, the energy were emitted at the same rate dur- 
ing the whole time, we would obtain for the energy of the lumi- 
nescence 2*911 watts. From the experiments of Professor E. 
Wiedemann we know that the transformation coefficient of radiant 
energy into luminescence is not more than about 4 per cent. 
{Wied. Annal ., Bd. 37, p. 233 ; Sitzungsber. d. phys. med. 
Gesellsch. zu Erlangen , 1888). Assuming the same proportion to 
hold good for the transformation of the energy of Rontgen radiation 
into luminescence, we find that the Rontgen rays producing the 
luminescence supply energy at the rate of 73 watts. This energy 
corresponds to that of 18 gram-calories per sec. Now the energy 
of the sun’s rays falling upon one square centimetre is equal to 
that of 0*035 g. Cal. per sec., so that if the Rontgen rays were to 
fall perpendicularly on a square centimetre, they would produce 
18-^0*035, i.e., 500 times the effect of the sun. Something like 
the same conclusion is reached if we take the result given by E. 
Dorn. He finds, for the total radiation during one second, 1*51 
mg. Cal. {Wied. Ann., Bd. 63, p. 175). Supposing, then, that the 
radiation here also lasts for xqVo second, we would get from his 
determination the value 1*51 g. Cal. per second, which nearly 
corresponds to that obtained by me. The energy of the cathode 
rays is much greater than this, being, according to the determina- 
tion of E. Wiedemann and H. Ebert {Sitzungsber. d. phys. med. 
Societat zu Erlangen , 1891), 1*4 x 10 5 times that of the sun. The 
coefficient of transformation of cathode rays into Rontgen rays 
must, therefore, be very small. 
In drawing a conclusion from this investigation, one must bear 
