Energy of Itontgen and Becqiierel Rays, &c. 247 



About 0'55 of the energy of the incident rays was absorbed in the grid. 

 Some of the energy of the rays was used up in exciting secondary 

 radiation at the surface of the platinum grid, but the amount was not 

 large, and was neglected in comparison with the total energy of the 

 rays. 



The rate of supply of heat to the grid area 92 '2 sq. cm. at a distance 

 of 26 cm. from the source of rays was 



0'00014 gramme-calorie per second. 



The total energy of the rays given out from the front surface of the 

 platinum antikathode (omitting absorption of rays in the glass of bulb, 

 in air and screens) was 



O011 gramme-calorie per second, 

 or 0-046 watt. 



The number of discharges per second was 57, and assuming 

 10~ 5 second* as the average duration of the rays during each dis- 

 charge, the maximum rate of emission of energy from the bulb 



= 19*5 calories per second. 



The heating effect of the sun's rays falling normally on 1 sq. cm. of 

 surface = 0'035 calorie per second. The maximum rate of emission 

 of energy from an X-ray bulb is thus 560 times greater than the energy 

 of the sun's rays at the surface of the earth. 



Some experiments were made on the heating effect of the rays, using 

 a thermopile, but it was found to be a very unsuitable instrument for 

 such a determination. 



Efficiency of a Fluorescent Screen. 



Photometric comparisons were made of the light from a fluorescent 

 screen with that of the standard Hefner- Alteneck amyl lamp, using a 

 Lummer-Brodhun prism. With a screen of platinocyanide of barium 



Intensity of light from screen _ 



Intensity of light from amyl lamp 



Tumlirzf has shown that the energy of the visible light from an 

 amyl lamp falling normally on 1 sq. cm. surface at unit distance 



= 0-00361 gramme-calorie per second. 



For X rays of- the same intensity as were used in the photometric 

 measurements, the energy under the same conditions 



= 0-0023 calorie, 



* Trouton, ' Brit. Assoc. Keport,' 1896. 

 t ' Wied. Annal.,' vol. 38, p. 640. 



