40 X)r. E. H. Cook on Experiments 



repute was a surprise to us. To find a well marked maximum 

 as the temperature rose, beyond which the loss decreased as 

 the beeswax and rosin composition softened was a second 

 surprise. To find so large a loss as the last observation 

 shows without the condensers giving way, and without any 

 very large leakage current, was a third surprise. 



In order therefore to verify these results by a totally 

 different method, and to determine as accurately as possible 

 the losses in some paraffin-paper condensers which we possessed 

 which showed relatively very small heating effects, we built 

 a special form of calorimeter, into which the condensers could 

 be placed and the heat directly measured. The calorimeter 

 was copied after the large respiration calorimeter which one 

 of us designed for experiments under the patronage of the 

 U. S. Government, and which is located at Wesleyan 

 University. The description of the calorimeter and the 

 results obtained with it are reserved for a subsequent com- 

 munication. We will only add that they fully confirm the 

 unexpected results obtained by the resonance method given 

 above concerning the dissipation of energy in beeswax and 

 rosin condensers. 



Wesleyan University, 



Middletown, Conn., July 1, 1898. 



III. Experiments with the Brush Discharge. 

 By E. H. Cook, D.Sc. (Bond.), Clifton Laboratory, Bristol* . 



[Plate I.] 



rt^HE ordinary phenomena which accompany the brush- 

 JL discharge are well-known, but in view of the recent 

 extension of our knowledge of electric discharges in high 

 vacua, it seemed desirable to study the subject a little more 

 closely. The following experiments have been made with 

 this object. 



Most of the results have been obtained with an ordinary 

 Wimshurst machine with 15-inch plates, but they have also 

 been produced with the discharge from an induction-coil, as 

 well as, though less readily, with a plate frictional machine. 



In experiments requiring the production of the brush for 

 a short period the machine was turned by hand, but where a 

 long-continued effect was desired, motion was obtained by 

 the use of one of Henrici's hot-air motors. The number of 

 revolutions of the plates was counted by means of a tacho- 

 meter, and the number of volts was taken as being about equal 



* Communicated by the Author, having been read before the British 

 Association at Bristol, 1898. 



