Intelligence and Miscellaneous Articles. 237 



(1) Ten Experiments with alternately opposite rotation. In each, 

 three readings, of which the middle one was made with the 

 electrification of the disk opposite to that of the first and 

 third. 

 Mean difference of the position of equilibrium, in 



scale-divisions , 6-735 



Spark-length _ . . . . 0-28-L5 



Electrodvuamic force acting on the astatic pair — 



observed 0-00000327 



calculated, M. 0-00000337 

 W. 0-00000311 



(2) Pour experiments, the same. 



Difference of the position 7" 50 



Spark-length 0-2955 



Eiectrodynamic force — observed 0-00000317 



calculated, M 0-00000349 



W 0-00000322 



(3) Five experiments, the same. 



Difference of the position '. 7*60 



Spark-length . 0-2926 



Eiectrodynamic force— observed 0-00000339 



calculated, M 0-00000355 



W 0-00000328 



The accordance may be looked upon as satisfactory in the 

 measurement of a force which amounts to only 577 od "o °^ ^ ne f° rce 

 of the earth's magnetism, since in two of the series the observed 

 values fall between those corresponding to the different measured 

 values of Weber's constant. 



As regards the signification of these experiments for the theory 

 of electrodynamics, they correspond to the hypotheses of the theory 

 of W. "Weber ; but they can also be referred to Maxwell's or to the 

 potential-theory which takes account of the dielectric polarization of 

 the insulators. The volume-elements of the stratum of air situated 

 'between the resting and the moved plates suffer continual dis- 

 placements in the direction of a rotation round radially directed 

 rotation-axes. The existing dielectric polarization of these elements 

 will therefore in each material element continually change, while 

 retaining in space the same direction normal to the surface of the 

 electrified disks. The arising and disappearing components of this 

 polarization would constitute the current which is indicated by the 

 astatic pair of needles. — Monatsbericht der Icon, jpreuss. Akademie 

 der Wissenschaften zu Berlin, 1876, pp. 211-216. 



NEW FORM OF COMPENSATING PENDULUM. 

 BY J. LAWRENCE SMITH, LOUISVILLE, KY. 



In the construction of this new form of compensating pendulum, 

 I have taken advantage of the very great expansibility of that com- 

 bination of sulphur and caoutchouc known as vulcanite or ebonite. 

 Its coefficient of expansion is known to approach that of mercury 

 in the ranges of temperature from 0° to 70° C. 



