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V. On a new Method of investigating the Composite Nature of 

 the Electric Discharge. By Alfred M. Mayer*. 



TN 1842 Professor Joseph Henry f observed that when a 

 needle was placed in a helix and magnetized by the dis- 

 charge of a Ley den jar, the direction of the polarity of the 

 needle varied with the "striking-distance" of the jar; and 

 these observations led Henry to the discovery that the discharge 

 was multiple and oscillatory in its nature. In 1862 Fedder- 

 senj confirmed Henry's discovery, on examining the nature of 

 the discharge by means of a revolving mirror. Subsequently 

 Rood (in a series of classical researches, published in Silliman's 

 American Journal, in 1869, 1871, 1872) studied the multiple 

 character of the discharge of the inductorium by means of ro- 

 tating disks perforated with narrow radial slits. In 1873 

 Cazin § also investigated the discharge with the rotating disk. 

 The method I have devised leads us directly, by the simplest 

 means, to phenomena which cannot be revealed by either revol- 

 ving mirror or rotating disk. The first method that occurred to 

 me was to attach a delicate metallic point to a vibrating tuning- 

 fork, and to send the discharge from this point through lamp- 

 blackened paper to a revolving metallic cylinder on which the 

 paper was stretched. We can to some extent analyze the elec- 

 tric discharge, in these conditions, from the series of perfora- 

 tions left in the paper in the trail of the vibrating fork. This 

 method, though beautiful as an illustration, is useless as a 

 means of investigation ; for the metal cylinder, the paper, and 

 the fork form a species of Ley den jar, which is always in the 

 circuit of the particular discharge whose nature you would 

 investigate. The above method, though original with me, 

 cannot be claimed as my own, having recently found that it was 

 devised by Donders||, and has been used in an investigation by 

 Nyland^j". To get rid of inductive action in the registering- 

 apparatus, I devised the following method: — A cylinder is 

 covered with thin printing-paper; and the latter is well black- 

 ened by rotating the cylinder over burning camphor. The 

 paper is then removed from the cylinder, and cut into disks 

 about 15 centims. in diameter. When one of these disks is re- 



* From Silliman's American Journal for December 1874. 



t Proc. Amer. Phil. Soc. 



\ tt Ueber die electrische Flaschenentladung," Pogg. Ann. vol. cxvi. 

 p. 132. 



§ Journal de Physique, vol. ii. p. 252. 



l| Onderzoekinyen yedaan in het Physioloyisch Laboratorium der 

 Utrechtsche Hooyeschool, 1868-69. 



*|| Archives Ne'erlandaises des Sciences exactcs et naturelles, vol. v* p. 292. 



