constructed by Mr. Ritchie of Boston, U.S. 467 



The primary wire is No. 9 gauge^ the helix 15 inclies in 

 length with three courses, the length about 150 feet; the inte- 

 rior bundle of wires 18 inches long, about 1| inch diameter of 

 annealed iron wire of No. 16, annealed with great care, having 

 been a fortnight in cooling. 



The primary wire has a cover of gutta percha y (jth of an inch 

 in thickness, ])assing through the basement to a plate of the 

 same, to which it is united ; over this gutta-percha coating a glass 

 tube passes. 



The secondary helix is divided into three bundles, each 5 inches 

 long, wound on cylinders of gutta percha y ^th of an inch thick ; 

 the wire in the upper and lower is of No. 33 gauge, each 25,575 

 feet ; the middle one is of No. 32, 22,500 feet, forming a total 

 length of 73,650 feet; the stratum of wire is perpendicular to 

 the length of the helix, and the wire is wound over with silk. 



The condensers are of varnished tissue-paper of three thick- 

 nesses between each stratum of foil ; thei"e are three condensers, 

 with surfaces of about 50, 100 and 150 feet; by means of screws 

 these can be used separately or combined. 



The contact-breaker is raised by means of a ratchet-wheel 

 turned by the hand, which acts on a spring, so that the platina 

 surfaces touch firmly. 



The upper platina has a screw and binding nut ; the hammer 

 has also its screw and binding nut : the hammer must not bear 

 too heavily, and care must be used to adjust the screws so that 

 the ratchet-wheel works well. 



It will be observed from the preceding description, that the 

 manner of breaking contact, or the disruption of the primary 

 current, is different from the plan used by Kuhuikorff or Fou- 

 cault in Paris, or by Bentley or Hearder in this countiy ; for the 

 exhibition of the ph^enomena of stratification their arrangements 

 are preferable, as in manipulating by means of a ratchet-wheel 

 it is difficult to obtain unifoi-mity of action ; but that of Ritchie 

 enables us to obtain the maximum effect due to the magnetization 

 of the iron core, to produce which, time is an important element. 



When the handle attached to the ratchet-wheel is turned very 

 slowly, the contact with the primary current is prolonged, and 

 the iron core consequently becomes highly magnetized; the 

 suddenness of the break instantaneously developes the entire 

 force of the induced discharge, not only giving sparks of great 

 length, but of a very remarkably dense character, the main line of 

 discharge being surrounded by a sort of burr; if the velocity 

 of the rotation is gradually increased, the discharge as gradually 

 assumes the white luminous character of a long spark taken 

 from the prime conductor of an electric machine, while, if tlie 

 velocity of rotation is still further increased, the luminous 



