( 323 ) 



The conditions of a short period of oscillation combined with a 

 relatively high intcnuil resistance are fulfilled by oidy one instrnment 

 besides the slriiijj,- gahanometer, as far as is known to nie, namely 

 by the oscillograph. Here the (himping is elfected hy means of oil 

 which is heated '). 



The temperature of the oil determines its viscosity and the regidatioji 

 of the degree of dani[)ing is conseipiejitly obtained in the oseillograpii 

 by regulating the temperature of the oil. it is (h)ubtful whether the 

 instrument would greatly gain in practical usefulness if the oil with 

 the heating arrangemein wei'e done away with aud replace(l by a 

 condense)". 



In the strinu' üalvanomeler the comlenser method will be success- 

 fully a[)plied in cases where it is desired to measure variations of 

 current of ^■ery short duration. Taking a very short and strongly 

 stretched (piartz-thread, it will be {)Ossible to obtain deflections wiiose 

 quiclvuess leaves little to be desii-ed. Without a C(mdenser these would 

 be useless for many [)ur[>oses on accouin of the oscillations, \vhereas 

 now they may become useful for a numl)er of i)hysical and electro- 

 technical investigations by a judicious damping. In these cases the 

 string galvanometer will for equal quickness of deflection a])[)ear to 

 be a much more sensiti\e ajiparatus than the oscillog)'apli. 



Also in a iuiml)er of electrophysiological investigations we can 

 avail ourselves of the condenser method, ^^ hile the study of sounds 

 will be particularly facilitated by it. I hope to make a nearer com- 

 munication on this subject in a following paper. 



Physics. — " D/.spcrsiou haiuls in tJw sjn'ctra of ó Ornmis uml 

 Nova Perser. \\\ Prof. W. H. .Iilhs. 



When light, giving a continuous spectrum, passes through a 

 selectively alrsorbing, non-homogeneous mass of gas, the spectrum of 

 the transmitted light contains places wliicii, according to circumstances, 

 may contrast as bright or as dark regions with their surroimdings'). 

 Though resembling emissi(tu aud absorption lines, tliese bands have 

 a wholly different origin. They are due to anoujahnis (lisj>ersion 

 and, therefore, the name dispcrs'nni JkiikIs has been suggested for 

 them '). 



1) Also a mixtufc of two ]i(iuiti.s is u.<cd, ul' wliich one has a great, the ullier 

 a small visco.^ity. Tlie mixtiiie is so clioson llial the desiied viscosity is just (»l)lained. 

 -) Proc. Hoy. Acad. Amst. II, p. 580 (11)00). 

 ■•) Proc. Roy. Acad. Amst. VII, p. 134—140 (1904). 



