Physics. — "On Centres of Luminescence and Variations of the 

 Gas Pressure in Spectrum Tubes at Electrical Discharges'' II.') 

 Bj Dr. L. Hamburger. (Communicated by Prof. H. A. Lorentz). 



(Communicated at the meeting of October 28, 1922). 



§ 1. Introduction. 



Experiments tnade by tlie author in 1916 showed that continuous 

 current-discharges when passing through not too rarefied gases, gave 

 rise to differences of pressure, the value of whicii, with sufficient 

 current density can amount to tliirty per cent of the total pressure. 

 A first communication on this subject appeared in tlie author's thesis 

 for the doctorate in the beginning of July 1917*). In these investi- 

 gations such variations of pressure were observed in numbers of 

 gases of very different natures, as aigon, neon, lielium, nitrogen, 

 hydrogen; it was found tliat the effects observed are very great in 

 argon, hardly perceptible in hydrogen, and it was seen that the 

 pressure effect must increase with the intensity of the current (loc. 

 cit. p. 94), and with the root of the moleculair weight (loc. cit. p. 107). 



Four months aftei' the publication of this Thesis for the Doctorate 

 F. Skaupy') published a short paper, in which he mentioned differences 

 of pressure in continuous current discharges observed by him (oidy) 

 in the case of noble gases; these differences of pressure were small 

 compared with the effect found by us owing to the small current 

 density applied by him. 



In April 1920 the author of this communication ') published some 

 further theoretical views and quantitative calculations about the 

 effects found, F. Skaupy confining himself in the course of the same 

 year to some qualitative remarks'*), which indeed referred more to 

 the phenomenon of elecfro-striction, which in our opinion can only 

 play a subordinate part. 



Finally in the middle of 1922 there appeared a publication by 

 A. RtJTTENAUER ^) ou ail important experimental investigation, in 



1) Cf. for f : L, Hamburger, These Proc. Vol. XXlil N». 2 and 3, p. 379. 



2) L. Hamburgkr, Thesis for the doctorate. Delft 1917. Gf. These Proc. 20, 

 1043 (1917). Zeitschr. f. Wissensch. Phot., 18, 1 ('19). 



*) F. Skaupy, Verh. d. Deutsch. Phys. Ges. 19, 264 -'67. Nov. Heft, '17. 

 *) F. Skaupy, Zeitschr. f. Physik 2, 215. Aug. Heft, '20. 

 6j A. RüTTENAUER, Zeitschr. f. Physik 10, 269—274 ('22). 



30 

 Proceedings Royal Acad. Amsterdam. Vol. XXV. 



