Prof. Thomson on the Measurement of Electrostatic Force. 233 

 Copper and Tin. 



Feb. 23. — Sir Benjamin C. Brodie, Bart., President, in the Chair. 



The following communication was read : — 



" Measurement of the Electrostatic Force produced by a Daniell's 

 Battery." By Professor William Thomson, F.R.S. 



In a paper U On Transient Electric Currents," published in the 

 Philosophical Magazine for June 1853, I described a method for 

 measuring differences of electric potential in absolute electrostatic 

 units, which seemed to me the best adapted for obtaining accurate 

 results. The "absolute electrometer" which I exhibited to the British 

 Association on the occasion of its meeting at Glasgow in 1855, was 

 constructed for the purpose of putting this method into practice, 

 and, as I then explained, was adapted to reduce the indications of 

 an electroscopic * or of a torsion electrometer to absolute measure. 



The want of sufficiently constant and accurate instruments of the 

 latter class has long delayed my carrying out of the plans then set 



* I have used the expression " electroscopic electrometer," to designate an 

 electrometer of which the indications are merely read off in each instance by a 

 single observation, without the necessity of applying any experimental process of 

 weighing, or of balancing by torsion, or of otherwise modifying the conditions 

 exhibited. 



Phil Mag, S. 4. Vol. 20. No. 132. Sept. 1860. R 



