THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



SEPTEMBER 1869. 



XIX. On the Construction of the Galvanometer used in Electrical 

 Discharges, and on the Path of the Extra Currents through the 

 Electric Spark. By E. Edlund*. 



I. 



YXJ"HEN an electric discharge is passed through a galva- 

 » * nometer in which the individual coils are well insu- 

 lated, it frequently happens that the position of equilibrium of 

 the needle is altered, and that this alteration lasts even after the 

 discharge. This disadvantage may be greater or less, according 

 to the construction of the galvanometer and the distance from 

 the coils to the moveable parts of the instrument, while the 

 quantity and density of the discharged electricity moreover exert 

 great influence in this respect. If the electrical discharges are 

 very powerful, it may happen that the galvanometer becomes 

 quite spoiled for accurate determinations of the discharge. 



There are several causes for this imperfection of the instru- 

 ment in question. It is well known that strong discharges can 

 bring about a change in the distribution of magnetism in the 

 magnet. The electrical shock can make the magnetic distribu- 

 tion stronger or weaker, or even invert the poles, or change the 

 line of connexion between them. If the galvanometer has an 

 astatic system, the electrical shock may easily alter the ratio of 

 the strength of the magnetisms in the two needles, by which the 

 delicacy is altered, and sometimes a change ensues in the posi- 

 tion of equilibrium of the system of needles. Hence a galvano- 



* Translated from PoggendorfF's Annalen, No. 3, 1869. 

 Phil. Mag. S. 4. Vol. 38. No. 254. Sept. 1869. N 



