352 Intelligence and Miscellaneous Articles. 



THE ENERGY OF THERMAL RADIATION AT A WHITE HEAT. 

 BY O. TUMLIRZ AND A. KRUG. 



The authors endeavoured to determine the energy which a pla- 

 tinum wire, heated by the current, gives off as light ; and, in the 

 first case, indirectly, by comparing the total quantity of heat im- 

 parted by the wire to a calorimeter with the energy imparted by 

 the work of the current. 



The difference found did not exceed the magnitude of the pro- 

 bable errors of the two determinations ; by which on the one hand 

 Joule's law was confirmed afresh, and on the other hand the loss of 

 energy by radiation is infinitely small in comparison with the total 

 loss of heat. The internal conduction in the wire plays an im- 

 portant part. In the course of this set of experiments it was 

 found that the disintegration of the platinum heated by the current 

 must have a disturbing influence over all such experiments ; it 

 makes the surface rough and thus increases the emissive power. 



In order to measure directly the energy of radiation the authors 

 used an air- thermometer specially constructed for the purpose, the 

 theory of which is fully described and discussed. 



The greatest radiation obtained represented an energy of 0*944 

 calories per square centimetre per second. 



If we assume with Tyndall that the ratios of the energy of the 

 visible to that of the whole spectrum is as 1 : 24, it follows that 

 the energy of radiation corresponding to the light can heat 42 mg. 

 in a second through 1° C. ; and experiments made previously by 

 the authors showed that, in the brightness of a platinum wire 

 equivalent to the amyle-acetate unit of light, 0*00326 gramme- 

 calorie were radiated in each second from a square centimetre. — 

 Wiener Berichte, vol. xcvii. p. 1521 ; Beibldtter cler PhysiJe, vol. xiii. 

 p. 499. 



CALCULATION OF THE MECHANICAL EQUIVALENT OF LIGHT 

 FROM THE EXPERIMENTS OF JULIUS THOMSEN. BY 0. TUMLIRZ. 



The author reverts to the experiments published in 1865 by J. 

 Thomsen in Poggendorff's Annalen, vol. cxxv. p. 348, in which a 

 bulb filled with warm water was placed at a certain distance from 

 a thermopile ; and thus various flames were placed at the same 

 distance, the total energy of radiation of which was found from 

 the indications of the galvanometer, the thermopile having been 

 graduated in the first experiment on the basis of Dulong's law of 

 radiation. By interposing a layer of water the rays of heat were 

 cut off, and the proportion of the radiant energy due to light-rays 

 was calculated. On the basis of the numbers given by J. Thomsen 

 the author, after accurately defining the unit of light, calculates the 

 radiation corresponding to the photometric unit of light at 0'0056 

 grm. cal., or the amount of work at 1 gr. x240 centira. 



In this the flame of a sperm-candle which burns 8-2 grammes in 

 one hour is taken as unit. — Wiener Berichte, vol. xcvii. p. 1625 

 (1888) ; Beibldtter der Pliysik, vol. xiii. p. 500 (1889). 



