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Physiology. — ''On a vpw method of dam jung Ofscillatm'y defiectionfi 

 of (I (/(i/rdiiomc/cr''. l>y 1^'of. W. EiNTHOVEX. 



(Communicated in the meeting of September 24, 1904). 



In a mimber of investigations, reqniring the nse of a galvano- 

 meter oi' electrometer, it is desirable to (Uimp \he oscillatory deflect- 

 ions shown by most of these insd'nments nn<Ier many circumstances. 

 Either mechanical damping is ap|ilied or electromagnetic damjnng 

 or both are cojnbined in order to obtain a strongei' effect. 



In some iiisti'nments, e.g. the DErRKZ-D'ARsoNVAi, galvanometer, in 

 which the coil is movable in a sfationary magnetic field, the electro- 

 magnetic damping may without any special arrangement be so great 

 that the deflections have lost their oscillatory character and have 

 become quite dead-beat. The movements are thereby i-etarded. This 

 retardation may l)e very considerable and so become troublesome, 

 even to such an extent that the instrument becomes impracticable. 

 Means of diminishing the damping are then applied, e.g. l»y iucreasing 

 the resistance in the galvanometer. 



In (H'der to apply electromagnetic damping in a needle-galvano- 

 meter the rotating magnetic system is to a greater or less extent 

 enveloped by a mass of pure copper in which during the motion 

 of the needles damping vortex currents are raised. 



Mechanical damping is appbed as li(pnd or air dampiug, thin 

 plates of aluminium or mica or insect wijigs l)eing often used. 



The method of damping to Ite described in this paper is entirely 

 different fiom the methods just mejitioned. It consists in inserting 

 a condenser between the ends of the galvanometer wire as is indic- 

 ated in fig. J. In the figure 

 E represents a source of current 

 by means of which an arbitrary 

 potential difference can be esta- 

 blished between P and 1\. G 

 is the galvanometer and C the 

 condenser. 



The action of the condenser 

 Pig_ 1, is most easily understood by 



assuming' the mass of the mo\ing parts of the galvanometer to be 

 zero and the eventual causes by which the motion is damped to 

 tend to zero. If under these conditions the capacity of the condenser 

 is zero, when a i)olential difference between P and 1\ is suddenly 

 established, the galvanometei- will also at once assume the corre- 



