25. Improvements in Measurements with Quadrant 



Electrometers. 



By V. H. Jackson, M.A., and A, T. Mukerjee, M.A 



[Read at the first Indian Science Congress, January 15th, 191 4. J 



[With Plate XXIII.j 



The difficulties connected with the use of quadrant elec- 

 trometers in India are well known. It would be hard to suggest 

 a more unfavourable climate for accurate electrostatic work 

 than that e.g of Patna, where a period of two or three very 

 hot months during which everything becomes covered with 

 dust is succeeded by another of three or four months in which 

 the air is practically saturated with moisture and the labora- 

 tory temperature usually remains between 28° and 34 C. 

 Even if it were worth while for special reasons, the older type 

 of Kelvin quadrant electrometer could scarcely be concerted 

 under any circumstances into an instrument which would work 

 satisfactorily under such conditions, owing to the troubles 

 connected with its glass insulation. Though electrometers 

 of the Dolezal k type are much more simple in use as well as 

 more sensitive, they do not give satisfactory results in India 

 without special precautions, and we believe that for this reason 

 their use in physical laboratories in t us eountry is more limited 

 than is desirable in view of the increasing importance of electro- 

 static measurements. 



We have been workii w 

 of the Patna College at intervals extending over more than 

 four years, and the object of this short paper is to show that 

 a few comparatively simple additions to the electrometer are 

 all that are necessary to render it capable of very accurate 

 work even during the dampest weather of the monsoon. These 

 additions are required (I) to secure greater accuracy in the 

 observations, and (2) to maintain high insulation under all 

 circumstances. These may be discussed separately. 



(1) Improvements in accuracy of measurement. 



It is unnecessary to elaborate the point that no measure- 

 ments can be trusted unless all keys and connections which are 

 used are efficiently screened from electrostatic disturbances. 



In electrometer work as in many other electrical measure- 

 ments it is advisable, especially in India, to depend as far as 

 possible on air for insulation and solder for contacts. 



• The most serious practical difficulty is the slight shift ot 

 the zero of the electrometer which is usually noticed when one 



