XL VII. • On a powerful Form of the Induction Coil, with some new 

 Statical and Thermal Effects of the Induced. Cttrrent. By 



Jonathan N. Hearder, Phjmmth^. > ^^^ oiju^u^^ i 



ON reading in the Philosopliical Magazine for January 1855, 

 an account of the very interesting experiments performed 

 by Prof. Grove with a powerful induction coil constructed by 

 M. RuhmkorfF of Paris, I immediately made inquiries respecting 

 the instrument, bat learnt that its construction was such, every 

 part being thoroughly imbedded in melted shell-lac, that nothing 

 was known of its internal arrangement. Having often promised 

 myself to make an instrument of the same kind, I proceeded at 

 once to act upon known principles in the construction of an induc- 

 tion coil, in which the secondary wire should be, as far as prac- 

 ticable, perfectly insulated, taking care at the same time to com- 

 bine with it the facility of removing and relaying it to correct 

 errors or repair injuries. 



My first attempt was eminently successful, since I produced 

 effects far exceeding those of M. Ruhmkorff's, with about one- 

 third of the quantity of secondary wire reported to be contained 

 in his machine. In March of the present year, I delivered a 

 paper on the subject to the members of the Plymouth Institution 

 and Devon and Cornwall Natural History Society, and then first 

 exhibited the machine in public. Subsequently in the same 

 month it was also exhibited before the members of the Plymouth 

 Mechanics' Institute by an eminent electrician of London, who, 

 when lecturing on the subject of the induction coil, availed him- 

 self of the opportunity of comparing it with one of M. Ruhm- , 

 korff's machines, and who at once gave his decision in favour of 

 my arrangement. I should have published a description of it at 

 the time, but having furnished him with minute particulars of 

 the construction of my apparatus, together with my views respect- > 

 ing the scientific principles involved in its action, for the purpose 

 of insertion in a new work on electricity which he had then 

 almost ready for publication, I promised not to do so until his 

 work was out. It has not, however, yet appeared; and I have, 

 now learnt that the same gentleman has recently delivered a lee- , 

 ture on the induction coil at one of the scientific institutions of 

 the metropolis, in which he brought forward a machine professing 

 to be an improvement on M. Ruhmkorff's apparatus ; and as it is 

 almost identical in construction and arrangement with mine, I 

 have felt some little surprise at his not having made the slightest 

 allusion to the fact of my having constructed one prior to the, 

 one which he had brought forward, particularly since at his own 

 especial request I had refrained from publishing any particulars 

 of my own arrangement. In the course of an extended series 



* Communicated by the Author. 

 Phil. Mag. S. 4. Vol. 12. No, 80. Nov. 1856. 2 C 



