520 On an Improved Construction of Ruhmkorff^s Induction Coil, 



an arc of flame passes the interval, and fuses electrodes present- 

 ing twenty times the sectional area of the wire from which the 

 current is produced : the flame can at the same time be acted 

 upon by a permanent magnet in the same manner as the voltaip 

 arc. This heating power appears to depend, not upon the quan- 

 tity of electricity passing, but upon the resistance it can over- 

 come ; consequently the thermal eflfects disappear in vacuo, to be 

 reproduced upon the gradual admission of air or other resisting 

 media. 



My induction apparatus differs from Ruhmkorff^s in three 

 important parts of its structure: flrst, in the method of insu- 

 lation; secondly, in the contact breaker; and thirdly, in the 

 formation of the condenser. Ruhmkorff, as your readers are 

 aware, insulated his secondary wire with shell-lac; but as this 

 substance, though an excellent insulator, is liable to crack, I have 

 adopted gutta-percha tissue for the insulation of my wire; and 

 I apply it in the form of ribbon an inch wide, which I obtain by 

 cutting slices from a firm roll of that substance; four or five 

 layers are necessary between each layer of wire, as the current 

 from a single layer is sufficiently intense to strike through one- 

 tenih of an inch of air. 



The contact breaker is a most important part of the apparatus, 

 for without the one I have contrived I do not obtain nearly so. 

 great a quantity of static electricity. It consists of a strong 

 steel spring, fastened firmly at one end, and having the platinum 

 contact piece in the centre, behind which is a piece of iron to be^ 

 attracted by the iron core; at the other end of the spring is a 

 screw, by which I can force the two contact pieces together with 

 a force of one ounce^to ten pounds; the steel spring therefore^ 

 vibrates from its centre, and it is only when the whole of the 

 battery current has traversed the primary wire that the iron core 

 has sufficient power to draw the two contact pieces asunder. It 

 may be interesting to state, that the condenser has not the slight- 

 est effect on the guaaliiy of electric force developed in the second- 

 ary wire, but increases the intensity to an enormous extent; and 

 as it is better to have it as large as possible, I have formed mine 

 of 120 sheets of tinfoil, 6x12, placed between double that num- 

 ber of varnished sheets of paper, the alternate sheets of foil being 

 brought out and soldered to appropriate binding-screws. The 

 length of secondary wire in the coil described is 2 miles, and its 

 gauge No. 35. The primary helix is formed of 30 yards of 

 No. 14 wire, and is wound on an iron wire core 9 inches long 

 and If inch diameter, in which is placed as an axis an iron rod 

 to support the coil, which I place in a box constructed for that 

 purpose. 



Such, then, is the very slight description I have to offer of an 



