M. B. W. Feddersen on the Electric Spark. 503 



deration of this subject. I feel some degree of satisfaction in 

 finding that the non-luminous condition of the planets has been 

 recently urged as an objection to ray views, as a disposition to 

 give them a fair test is apparent ; and I have reason to hope that 

 it will lead to a careful examination of those facts on which I 

 mainly rely for the confirmation of my theory on solar light. 



Cincinnati, Ohio, 

 November 29, 1858. 



LVIII. Contributions to the knowledge of the Electric Spark. 



By B. W. Feddersen*. 



[With a Plate.] 



IT is not on the whole surprising, that the investigation of 

 electrical phsenomena and their laws presents the greatest 

 difficulty in those cases where electrical motion arises from 

 electrical rest and the reverse. On the contrary, from analogy 

 with the other provinces of physics, we should be inclined to 

 pronounce the complete explanation of this state of transition 

 to be one of the most difficult problems of electricity. Although 

 it has not been proved that the electric spark gives in its path a 

 direct and undistorted representation of the electrical discharge 

 which produces it, yet the two stand in such intimate connexion, 

 that the study of the optical phsenomena in the electrical spark 

 must be of use in gaining a knowledge of the mode of discharge. 

 The study of the spark, it is true, also offers great difficulties. 

 The only possible method of obtaining a direct analysis of the 

 spark, appears to me to be the conversion, by a mechanical 

 motion, of the intervals of time into intervals of space. The ro- 

 tating mirror which I judged most suited to my purpose is 

 based upon this principle. Although in my experiments I em- 

 ployed an electro-magnetic rotation apparatus to obtain an ap- 

 proximately uniform motion during short spaces of time, yet 

 in one important point my arrangement diflers from that of 

 Wheatstone. I effected the discharge, namely, when the appa- 

 ratus was in one particular position, by means of a slipping spring, 

 thus furnishing every such discharge during its whole continu- 

 ance with a circuit of as constant a nature as possible. After 

 converting, by means of such an arrangement, intervals of time 

 into intervals of space, the next problem is to devise a method 

 for the measm-cment of the latter. If, now, for this purpose the 

 mirrored image of the spark was removed beyond the distance 

 of distinct vision, and a scale was held at the same distance from 

 the eye, in such a manner that the image appeared to fall upon 

 * Translated by Dr. F. Guthrie, from PoKgendorrt's Annalen, vol. ciii. 

 \). CO. 



