( 318 ) 



of the plate jiiiswers better tlie cojidiliuns required Ihaji liu. o. hut 

 tlie great practical importaiice of ihe inefhod is exactly that it is 

 possible to damp the oscillations and at the same time to retard the 

 deflection as little as possible. When measurements are made one 

 will always try to choose 7' such that exactly the limit between 

 oscillatory and aperiodical motion is attained. In this case T is i-ela- 

 tively small and m and r may no longer be neglected. 



The qnestio]! now arises liow for known values of m ajid /• the 

 value of T must be calcidated \\\ oi-der to obtain the limiting case 

 mentioned . 



In passing it be remembered that with the capillary electrometer 

 the damping of the motion of the mercury meniscus is also composed 

 of mechanical fiiction and of retardation by capacity.') And from 

 the combination of these two results a motion which can be expre.ssed 

 by a simple exponential function either quite accurately or with 

 only small deviations. The resistance of air or licpiid damping as 

 well as electromagnetic damping influence the motion of a body 

 having mass, in exactly the same way as (•(»iiducti\e resistance in- 

 fluences the motion (»f electricity when a condenser is charged or 

 discharged. 



A simple reasoning will show, howevei-, that acUling a condenser 

 to the galvanometer has not always an inlluence on the movements 

 of the string of the same nature as an increase of the damping 

 forces which we called /'. 



Yov the addition of the condenser has the effect of a temporary 

 cliange of the active force. And the way in which the force is 

 increased or decreased from moment to moment is not determined 

 l)y the motion of the string, as the mechanical and electromagnetic 

 damping, but by the |)roduct of the conductive resistance and the 

 capacity ir' c = T. 



When applying the condenser method, the character of the motion 

 of the string near the limiting case of aperiodicity can only be 

 represented by a more or less complicated formula. T ha\e therefore 

 for this liuiitiug case preferred direct experinioutal determinatio]! of 

 the value of T to calculation. 



Some curves lia\e been I'eproduced which exemplify the motion 



1) Some investigators liave been of opinion tliat llio motion in tlie capillary 

 electrometer is dependent on tlie cliarge of the mercuiT meniscus only. But in 

 reality damping by mechanical fiiclion is much more active here. See Pfll-ger's 

 Arcli. f. d. gf's. Pliysiol. I>d. 711. p. 1. Ill00;and ,Onderzoekii;gen" Physiol. laborat. 

 Leyden, :2nd series, 4. 



