110 ANNUAL OF SCIENTIFIC DISCOVERY. 



and about l- r >-S diameter, composed of fine iron wire not larger than No. 22, 

 very carefully annealed. The primary wire should be of sufficient size to 

 carry freely the whole of the battery current, and of sufficient quantity to 

 thoroughly saturate the iron core with magnetism. For this purpose I use 

 three layers of one continuous No. 12 copper wire carefully annealed; if more 

 layers are used I find that the secondary wire is removed too far from the 

 magnetic influence. The secondaiy wire ought not to be larger than No. 35, 

 covered with silk, which must be laid on perfectly even and insulated from 

 the primary wire, and also from the layers of the secondary next to it. I 

 find the best insulating medium to be the thinnest gutta-percha made, and 

 which, I believe, to be the only gutta-percha sold which cannot be adulter- 

 ated; it is true that it has many minute preTorations, but by laying on, at 

 least, six thicknesses between each layer of wire, perfect insulation is secured. 

 The greatest care must be taken in protecting the ends of the layers so as to 

 prevent the sparks passing from one to the other. The condenser should 

 be, at least, fifty sheets of tin-foil of about one square foot in size. These 

 sheets must be separated from each other by three sheets of varnished paper 

 or gutta-percha tissue. Every alternate sheet of foil is connected together, 

 thus forming two poles, to be attached one to each side of the break. It may 

 l)e placed at the bottom of the stand or in a separate box ; the latter I prefer. 

 In developing the power of the machine, everything depends upon the con- 

 tact breaker, which should be capable of retaining contact until the whole of 

 the magnetism is obtained, and capable also of breaking contact as soon as 

 the smallest quantity is induced. These results are obtained in the break at- 

 tached to this instrument. The hammer is made to vibrate freely between the 

 core and the coil, and the brass screw terminating with the platina plate at the 

 back of the hammer, a very small amount of magnetism will be sufficient to 

 attract the hammer and so break the contact. If now I bring this screw 

 (placed half-way up the spring carrying the hammer) to bear upon the spring, 

 it will have the effect of pressing the tAvo platina plates together, so that it 

 takes a greater amount of magnetism to separate them. By this means I 

 can regulate the power of the instrument to the purposes for which it is 

 required. The batten' I employ is a five cells of " Grove's," with immersed 

 platina plates 5 * 3, having an exposed surface of 140 square inches. With 

 such a battery and a coil thus constructed, I can always insure sparks from 

 half an inch to four inches in air. The machine now exhibited contains six 

 miles of wire, and worked with the same battery, gives six and a quarter 

 inch sparks. The position which the induction coil is now taking in this elec- 

 trical age is one of considerable importance. It has awakened new philo- 

 sophical ideas, and is being successfully applied to practical purposes of the 

 highest advantage to mankind. For blasting purposes, a three-mile coil is 

 capable of firing fifty charges simultaneously. But, important as its present 

 position is, and successful as its past application has been, it is yet in its in- 

 fancy, and there can be little doubt that by patient perseverance machines 

 can be constructed that will obviate the necessity of employing such ponder- 

 ous machines, and still more ponderous batteries, as are now at work on the 

 Atlantic Cable. 



JAX'S IMPROVEMENT. In using Ruhmkorff's coils, damage is not unfre- 

 quently sustained by the electric spark forcing its way through the apparatus 

 itself, in place of passing between the poles. To avoid this, M. Jan has 

 devised a plan of plunging the apparatus in a non-conducting liquid, such as 

 the spirits of turpentine. The liquid filling the interstices of the coil, coil- 



