I. INDUCTION COILS. 311 



d. INDUCTION COILS. 



1303. RuhmkorfPs Coil. Frederick Guthrie. 



The current from a galvanic battery passing through a spiral of copper 

 wire magnetises the soft iron bars placed within it, which by their attraction 

 so move a steel spring as to interrupt the current. The current being thus 

 broken, the magnetisation ceases until the current is again restored. The 

 result is a very rapid making and breaking of the current in the spiral or 

 primary wire. Outside the primary are many miles of fine insulated copper 

 wire called the secondary wire. Connected with the primary by wires, one 

 on each side of the contact breaker, is a tin-foil condenser. This absorbs 

 the extra-current when the primary is broken, and serves to augment the 

 secondary when the primary is made. The interior magnetism acts in the 

 same direction. 



1304. Six-inch Induction Coil, and Browning's Spark 



Condenser, for obtaining spectra of metals by the induction 

 spark. John Browning. 



When using the spark condenser the amount of coated surface introduced 

 may be varied at pleasure, and the density of the spark thus regulated. 



13O4a. Apps' Patent Induction Coil, giving sparks of 

 17 in. in air, with a battery of five Grove's cells, platinum, 

 5x3 in. immersed. Alfred Apps. 



13O4b. Henry's Induction Coils. 



The Council of King* s College, London. 



13O4aa. Large Induction Coil, with thick secondary wire 

 (10^ miles in length), and improved form of contact-breaker 

 by which a long interval of contact is obtained. Horatio Yeates. 



This is wound on the plan proposed by Dr. Fergusson (in two divisions), 

 the secondary wire which is No. 32, B. W. G. is 1O| miles long. The primary 

 wire, No. 8, B. W. G. is wound in two laps. 



The condenser is composed of 70 sheets of tinfoil, 26 x 16, insulated with 

 paraffine paper. 



The contact-breaker, which is so formed as to give a long interval of 

 contact, is also furnished with an adjustment by means of which the coil can 

 be worked with a very small battery, and maximum results obtained with the 

 largest suitable battery. 



1305. Large Induction Coil, with Foucault's break ; will 

 give 18-inch sparks. A cube^of glass which was pierced by this 

 coil. M. Ruhmkorjff. 



1305a. Electric Necessaire, containing Ruhmkorff bobbins. 



M. Laiseau, jun., Paris. 



1306. Induction Apparatus for medical purposes. 



Keiser and Schmidt, Berlin. 



1307. Induction Apparatus for medical purposes. 



Keiser and Schmidt, Berlin, 



