462 Mr. J. M. Kuehne on the Electrostatic 



The experiment consisted of suspending two charged mica 

 or gelatine vanes fastened to the ends of a light rod, after 

 the manner of a very delicate torsion balance, inside and in 

 the plane of a large magnetized ring placed vertically, and 

 then reversing the magnetization of the ring synchronously 

 with the natural period of oscillation of the vanes. The 

 experiment was believed to have yielded positive results ; 

 but the fact that it was purely qualitative and that no data 

 are available for deciding whether the observed deflexions 

 were even remotely of the order of magnitude demanded by 

 theory makes it at least very doubtful if one or more of the 

 very numerous disturbing forces was not entirely responsible 

 for the effects observed. 



Cremieu* in 1900 published an experiment in which an 

 attempt at a quantitative determination was made. His 

 apparatus consisted of a charged disk of aluminium suspended 

 horizontally by a light glass frame between the flat ends of 

 two spools of wire, thus constituting a parallel plate con- 

 denser. A straight soft iron core passed through the two 

 spools and through a large hole in the suspended disk. The 

 frame supporting the disk was pivoted in jewelled bearings 

 set into the ends of the bar magnet, and was supported 

 partly by a very thin and long silver wire, partly by a float 

 ?e«sting-i4 a r vessel of water underneath. By reversing the 

 oii.ectien. o£ magnetization of the magnet alternately with 

 reversals of the charge? on the condenser, a steady deflecting 

 :r. omenta ;&houM be produced, whose value is 



; '" ; ' T "_^ Q_ 



;cC( ei _ ( ./", ' ^~ dt'Zir 9 



wnere Q< js the charge on the disk, expressed in electro- 

 magnetic units, and N the magnetic flux through the magnet. 

 With n reversals per second this becomes 



T wNQ 



7T 



Cremieu omits the factor 2tt in the denominator, and calcu- 

 lates a deflexion, as observed by a telescope and scale at 

 110 cm. distance, of 100 to 140 mm., whereas he is unable 

 to observe any deflexion whatever. From this he draws the 

 conclusion that no such electromagnetic effect exists. Ac- 

 cepting the value (6 to 8 X 10~ 4 c.G.s. unit) of the deflecting 

 moment calculated by Cremieu, it is by no means certain 

 that even the slight friction of the jewelled bearings would 

 * Comptes Rendus, cxxxi. p. 578. 



