502 Prof. Angstrom on the Intensity of 



fleetly determinate except T r If CO = a, CA = b, and T a , T& 

 denote the tensions along OB, AD, we have 



T _ A k tan a "] 

 a ~~a~ aJ~ f 



„ A h tan a 



>■, (9) 





from which it appears that either T a or T b may, if we please? 

 be made zero, provided the other be properly determined. 



The above results would also apply to a belt of a complete 

 cone, bounded by two circular sections. 



LI. Bolometric Investigations on the Intensity of Radiation 

 by Rarefied o Gases under the Influence of Electric Discharge. 

 By Knut Angsteom*. 



ONE of the peculiar difficulties attending the quantitative 

 determination of the amount of energy radiated by gases 

 in vacuum-tubes is the extreme feebleness of its intensity. 

 In his recent work in this field, executed at the Hochschule 

 at Stockholm, Prof. Angstrom attacked the problem by the 

 bolometric method, which, although leaving something to be 

 desired as regards sensitiveness, led to some important results. 

 Another obstacle lay in the well-known difficulty of obtaining 

 the gases in a state of such purity that the spectrum exhibited 

 by the discharge through them in a vacuum-tube showed no 

 foreign admixture, such as the carbon-bands seen whenever 

 grease is used for joining surfaces, or where the flame touches 

 in the process of soldering. 



The discharge-tube used for the most careful experiments 

 was thoroughly cleaned after soldering-in two electrometer- 

 terminals, and attaching two short lengths of tubing at right 

 angles near each end. The latter were to receive the elec- 

 trodes, whose construction required particular care. Into a 

 short capillary tube a piece of platinum wire was introduced 

 from one end and a piece of thoroughly cleaned aluminium 

 wire from the other. The tube was then heated so as to form 

 an air-tight junction between the two wires, and was then 

 fitted into a glass plate. After removing all grease the tube 

 covering the aluminium wire was cut off', so that the latter 

 acted as a perfectly clean electrode, and the glass plate hold- 

 ing it was fitted on to the short tube attached to the discharge- 



* Abstract from Wiedemann's Annalen, No. 3, 1893, by E. E. Founder 

 d'Albe, B.Sc, Koyal College of Science. 



