446 M. Van Marum on [Dec. 



•work on electricity. On his return from Germany, where he had 

 been in the army, he came to see me at my country house in 

 1810 on a festival, when it was not in my power to gratify his 

 desire of seeing our large Teylerian electrical machine. He then 

 eagerly entered into an ample detail concerning his theory of 

 electrical or electrochemical phenomena, which was entirely 

 founded on the old system of vitreous and resinous electricity, 

 according to which he endeavoured to explain aU electrical phe- 

 nomena, at the same time avaihng himself of chemical affinities, 

 which he made to act just according to his own imagination. 



The prejudice of this learned man for his theory, which, he 

 informed me, he was about to publish shortly, prevented me from 

 then opposing his arguments. I, therefore, contented myself 

 with inquiring whether he had read an account of the experi- 

 ments which I had made with the Teylerian apparatus. He 

 replied that he had once seen my pubhcation, and that the jour- 

 nals had communicated to him my experiments. 



Meeting him the following day at the Teylerian Museum, I 

 showed him the drawing of the electrical spark of the large 

 machine, and perceived that he either had not seen it before, 

 or had forgotten it. He began by putting questions which 

 plainly proved to me that he was doubtful whether all the branches 

 were turned on the same side as they were represented in the 

 figure. The temperature of the air happening to be then very 

 favourable for electrical effects, I replied by offering to con- 

 vince him of the truth of this direction of all the lateral branches 

 of anjelectrical spark to the same side. I then conducted him to 

 the new machine, invented and described by me in 1791, con- 

 sisting of a disk 31 inches in diameter, and placed in a room ia 

 the Teylerian Museum, where it is always in readiness for use. 



By means of this instrument 1 showed him that the rays 

 proceeding from a button placed in the lower part of the positive 

 conductor produce, in favourable weather, lateral sparks, which 

 are all directed towards the globe conductor which receives the 

 spark. I also showed him that when the same conductor which 

 has emitted the electric sparks, having been positively electri- 

 fied in its ordinary position, is made to touch the cushions 

 (which is accomplished by the movement of its semicircle), 

 and, when in this situation, deprived of its electric fluid, the 

 same button, which, in the first instance, emitted ramified 

 sparks, then produces no more sparks ; but that, on the con- 

 trary, if a similar button of copper be brought within about six 

 inches of the large globe of this conductor, one then perceives 

 proceeding from the button sparks of a similar length, which, as 

 well as those of the positive conductor, produce lateral ramifica- 

 tions, and these sparks differ singularly from those of the posi- 

 tive conductor, inasmuch as they have an opposite direction. 



After the French philosopher had thus evidently seen by 

 repeated experiments that all the lateral ramifications of the 



