48 Prof. A. M. Mayer on a new Method of investigating 



volved about twenty times per second, it is rendered very flat 

 by centrifugal action. It can then be brought between points 

 or balls, even when the latter are separated by no more than 

 f millim. When in this position, the discharge between the 

 points or balls perforates the disk and leaves a permanent 

 record of its character, of the duration of the whole discharge, 

 and of the intervals separating its constituent flashes and sparks. 

 To obtain the time of rotation of the disk, I use the method 

 invented by Young in 1807 (see his 'Natural Philosophy/ 

 vol. i. p. 191) ; that is, I present momentarily to the rotating 

 disk a delicate point which is attached to a vibrating tuning- 

 fork. The number of vibrations per second of this fork has been 

 determined to the last degree of precision by means of a break- 

 circuit clock, which sends at each second a spark from an induc- 

 torium through the fork's sinuous trace on blackened paper 

 covering a revolving cylinder. The axis of the sinuous line on 

 the disk is traced with a needle point; and then, on drawing 

 radii through symmetrical intersections of this axis on the sinu- 

 ous line, we divide the disk off into known fractions of time. 

 The disk is now removed from the rotating apparatus, and the 

 carbon is fixed by floating the disk for a moment on thin spirit- 

 varnish. When the disk is dry and flat it is centred on a 

 divided circle provided with a low-power reading-microscope ; 

 and the duration of the whole discharge, and the intervals sepa- 

 rating its components, can be determined to the 5-fl-Jon °f a 

 second. 



Many results have been obtained with this apparatus. I 

 defer their publication until I have carefully examined them 

 and have extended this research with the study not only of the 

 discharge of the inductorium, but also of the frictional machine, 

 of the Leyden jar, and of the Holtz machine, under every condi- 

 dion of charged surface and of striking-distance, and when the 

 current is flowing freely over a conductor and when it is doing 

 work. I here present, merely as examples of the value of the 

 method, the results I have obtained in three conditions of 

 experiment. 



1. Discharge of large inductorium* between platinum points one 

 millim. apart. No jar in the circuit. 



The platinum electrodes were neatly rounded and formed on 

 wire -j% millim. in diameter. After the discharge through the 

 rotating disk, nothing was visible on it except a short curve 

 formed of minute, thickly set white dots ; but on holding the 

 disk between the eye and the light, it was found to be perfo- 

 rated with thirty-three clean round holes with the carbon undis- 



* The striking- distance of this coil between brass points was 

 45 centims. 



