22 SIXTH REPORT. — 183(>. 



great attention since it is of importance to an exact theory of elec- 

 tricity. 



Tlie author submitted to experiment under various conditions, 

 two equal spheres and a circular plate of the same extent of surface, 

 each side to each side, and found their electrical capacities precisely 

 the same. Thus the result of the contact with the charged sphere 

 and a similar neutral sphere, or with a circular neutral plate, was 

 precisely the same. The same quantity of electricity disposed either 

 upon the sphere or plate, in connexion with the fixed baU of the 

 balance, evinced the same intensity ; and this intensity became also 

 equally diminished, whilst thus connected, whether the charged 

 body was touched with a sphere or circular plane of the same area. 

 The author does not pretend to question the faithfulness of Cou- 

 lombe's experiment, but considers his result embarrassed by the cir- 

 cumstances just mentioned ; more especially as he found, that when 

 the electricity was equally distributed upon the repelling discs of the 

 balance, and the square roots of the forces taken to determine the 

 respective quantities of electricity, then the apparent differences in 

 the capacities of the sphere and plate vanished ; he considers there- 

 fore that the traces of repulsion indicated by the balance did not in 

 Coulombe's experiment truly represent the ratio of the quantities of 

 electricity before and after the contact between the sphere and plate. 



These results were further verified by means of the attractive 

 forces, through tlie agency of a new electrometer, and which the 

 author exhibited and explained to the Physical Section at a former 

 meeting of the Association. The author next proceeded to consider 

 more at large the operation of the proof plane, and presented to the 

 Section the results of numerous experiments on tangent planes of 

 various degrees of thickness and extension, from which it appeared 

 that the indications of the proof plate might be so materially in- 

 fluenced by the circumstances of position, intensity of the charge, 

 thickness, and the like, as not always to become charged, either with 

 a similar quantity or in tlie ratio of the quantity of electricity with 

 the point of the electrified body to which it is applied. In treating 

 of the proof plane, philosophers have considered its action in more 

 than one point of view. Mons. Biot states that it takes up upon 

 each of its surfaces as much electricity as exists upon the point 

 touched, hence on removal it is charged with twice the quantity of 

 electricity as that of the corresponding superficial element. Mons. 

 Pouillet, on the contrary, considers the proof plane to be in precisely 

 the same state as the superficial element itself, and to be on removal 

 in the same condition as a similar portion of the charged body would 

 be, if actually taken out of its surface, that is to say, the electricity 

 would be first collected on one surface, and be subsequently expand- 

 ed on both ; each surface has therefore only half the quantity of the 

 superficial element, and the proof plane comes away charged with the 

 same quantity, but under a diminished intensity. The author deems 

 it worthy of further inquiry, whether the proof plane be really iden- 

 tical with an element of the charged surface, or whether it be merely 



