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XXXI. Note on the subject of a Paper by Prof. L. T. More .- 

 "On the supposed Elongation of a Dielectric in an Eleclro- 

 static Field " *. By Dr. P. Sacerdote f. 



PPOP. L. T. MORE, of the University of Nebraska, has 

 recently published an account of a series of experiments 

 in which he purposed measuring the elongation experienced 

 by a glass tube forming the dielectric of a cylindrical con- 

 denser when the condenser is charged. In none of his 

 experiments did he succeed in observing any elongation or 

 contraction of the tube : from this he concludes that no 

 electrical deformations of dielectrics exist, and that those 

 observed by Grovi, Duter, Righi, Quincke, &c. were only due 

 to disturbing causes. In the present note I shall show that 

 the conclusion to be drawn from Prof. More's paper is quite 

 different. By the very disposition of his experiments the tube 

 should not experience any appreciable elongation ; thus the 

 negative result of his experiments merely proves that they were 

 carefully performed. 



1. For the description of the apparatus I refer to Prof. 

 More's paper, merely recalling that it consisted essentially of 

 a glass tube A, 2" 5 mm. thick, and of two coaxial metal 

 tubes B' B /; , which constitute the armatures, the one B' 

 interior, the other B" exterior to A, from which they are 

 separated by an interval ; the arrangement for magnifying the 

 dilatation was such that one division of the micrometer eye- 



1*5 

 piece corresponded to an elongation of A of ™ micron t. 



First Experiment. — The space between B' and A, as well 

 as that between A and B' 7 , is filled with an insulating liquid ; 

 then, the armature B' being earthed, B" is charged by an 

 electric machine. In no case did Prof. More obtain any 

 displacement of the reflected image by the amplifying mirror. 



Second Experiment. — The cylinder B" is removed and 

 replaced by tinfoil 45 cm. long cemented on A. The space 

 between W and A is filled with acidulated water forming the 

 internal armature. Prof. More still obtained no elongation 

 or contraction, even on charging this condenser to high 

 potentials corresponding to sparks of 12 mm. to 20 mm. 

 between two brass knobs of 2 cm. diameter. 



* Phil. Mag. vol. 1. pp. 198-210 (1900). 



t Communicated by the Author. 



% I omit all criticism relative to the apparatus, although in my opinion, 

 for such small displacements, direct measurement by interference-fringes 

 is the only one that can be relied on, and it is in any case much prefer- 

 able to any mechanical process of amplification. 



