1813.] 



Imperial Institute of France. 



155 



of objecting to the theory its want of coincidence with experi- 

 ment, we ought rather to be surprised at the near approximation 

 of the formula and these experiments made more than twenty 

 years ago, and which M. Poisson details at the end of his me- 

 moir. In reality the difference never amounts to a thirtieth 

 part of the quantity to be determined. 



Hitherto M. Poisson has only considered a single excited 

 body, or several bodies touching each other in such a manner, 

 that the electricity may pass freely from one body to another. 

 He now shows how the analysis applies equally to the case when 

 the two fluids occur at the same time upon the surface of the 

 same body. He makes choice of two spheres, separated by a 

 very great interval, in respect to one of the two radii. If we 

 suppose that the sm.ail sphere is not electrified in tlie first place ; 

 but merely by the influence of the great sphere, we find that 

 the electricity, contrary to that of the great sphere, accumulates 

 towards the point that is least distant from it, while the similar 

 electricity accumulates on the opposite point. The contrary 

 electricities in these two points are almost equal, and the line 

 of separation differs little from the grand circle perpendicular 

 to the line that joins the two centres and divides the little sphere 

 into two equal parts. Calculation gives by means of very sim- 

 ple formulas, the quantity and the kind of electricity in each 

 point of the two surfaces. The memoirs of M. Coulomb fur- 

 nish no experiments to which these formulas may be directly 

 applied. But we find in them a curious fact which connects 

 itself with these formulas 5 and furnishes a new confirmation of 

 the theory. 



We shall not enter into any detail respecting this fact, for 

 "which we will refer to the Memoir of M. Poisson. We would 

 not even have undertaken the extract which has been just read, 

 were it not that this analysis of the labours of the Class is destined 

 to appear separately. For M. Poisson has himself prefixed to his 

 paper a clear and precise introduction, in which will be found 

 every thing necessary for a philosopher, who is not familiar wath 

 the transcendental calculus. This clearness which indicates a 

 mind superior to the subject, is equally conspicuous in the deve- 

 lopement of the analysis. He every where points out how far 

 his theorems agree with experiment. This kind of demonstration 

 would not be useless even though the truth of the fundamental 

 hypothesis were quite certain. It is the only one which can 

 ever give confidence to those who, though capable of calculating 

 a formula, are not able to follow its demonstration. It may en- 

 courage a taste for analysis by showing that it is a light capable 

 of dissipating the darkness which still covers very important parts 

 of physics. Our readers will learn with pleasure that M. Poisson 

 ^neans to continue his researches, and to extend them to morQ 



