A Study of Franklin s Experiment on Leyden Jar. 489 



small rise to 2*41 at 80° A. The present arrangement did 

 not permit of an accurate determination as to whether there, 

 was an actual discontinuity in the value of the dielectric 

 constant at the melting-point, or whether the change took 

 place in a small range of temperature. The former alternative 

 is probable, and the change is so represented in the graph 

 (% 2). 



Summary. 



A method is described for the determination of the di- 

 electric constants of liquid or solid substances by the aid of 

 triode valve circuits. The results obtained by this method 

 for the dielectric constants of methyl, ethyl, n-propyl, and 

 n-butyl formates, and the corresponding acetates at the 

 temperature of liquid air, are then given and compared with 

 the values obtained by other investigators at ordinary tem- 

 peratures. It is shown that at the low temperatures the 

 acid radicle apparently contributes but little to the value of 

 the dielectric constant. Results showing the dependence on 

 temperature of the dielectric constant of n-butyl acetate 

 throughout the range of temperature 292° A-80° A are also 

 given. It is found that the dielectric constant of this sub- 

 stance increases linearly with decrease of temperature down 

 to the melting-point, at which a sudden fall in the value 

 occurs, followed by a very gradual rise as the temperature 

 is further lowered. 



The author desires to express his indebtedness to Prof. E. 

 H. Barton, F.R.S., for the facilities afforded to him in his 

 laboratory, to Mr. C. F. Ward, B.Sc, for his kind assistance 

 in the rigorous purification of the materials used, and to the 

 Department of Scientific and Industrial Research for a grant 

 by the aid of which the above work was carried out. 



Physical Laboratory, 

 The University, 

 Leiden (Holland). 



LY. A Study of Franklin's Experiment on the Leyden Jar 

 with Movable Coatings. By Gr. L. Addenbrooke, M.I.E.E* 



TO understand the actions in dielectrics it is very 

 desirable to have a clear idea of the principles which 

 underlie electrostatic actions. For the most part these can 

 be found in text-books, but there is one respect in which 

 they are all defective, and that in connexion with one very 

 * Communicated by the Author. 



