406 



ELECTRICITY. 



the strength of the charge generated could be 

 estimated , and this is numerically expressed 

 for the various liquids so examined, 5.8 being 

 taken to represent the electro-motive force of 

 a single Grove's element. The generated 

 charges in case of some of the substances ex- 

 amined were as follows : Bromine, +400 ; 

 iodine, +90; ammonia, 200 ; alcohol, 10; 

 mercury, 75 ; water, 80 ; strong solution 

 of common salt, 400 ; caustic potash, +150 ; 

 strong nitric acid, +7.5; benzole and valerianic 

 ether, no effect. From a like series of experi- 

 ments on the development of electricity during 

 brisk effervescence of different liquids, the fol- 

 lowing results were obtained : with solution of 

 zinc in hydrochloric acid, 750 ; solution of 

 binoxide of manganese in hydrochloric acid, 

 150; solution of common salt in sulphuric 

 acid, +10. (" Proc. Roy. Soc. Edinb.," Feb. 

 1862.) 



Experiment with the Crural Nerve of Frog. 

 In this experiment, one of the first by which 

 Galvaui was enabled to lay the foundation of 

 that branch of electrical science now very 

 commonly bearing his name, of the two 

 metals employed one was made to touch the 

 nerve of the frog's leg, the other at the same 

 time the muscle ; and in the directions for re- 

 peating the experiment, this is the arrangement 

 usually laid down as requisite. If, however, 

 the upper end of the nerve be dissected out 

 from the thigh, and the metals be so placed that 

 both shall be in contact at one of their extre- 

 mities with this part, so that the current shall 

 pass through the nerve alone, the muscular 

 contraction and movement of the leg are 

 equally great. The experiment in this form is 

 conveniently performed by winding the sepa- 

 rated or free end of the nerve around one wire 

 of a galvanic cell or element, and then touch- 

 ing with the other wire any other point in the 

 exposed nerve, so as to pass the current through 

 the intervening portion. If the second wire 

 touch the muscle, this serves as a conductor, 

 and the contractions follow of course ; but the 

 preceding experiment appears to show that the 

 effect is due in reality to passage of the current 

 along a portion of the nerve. 



Electrical Phenomena of Vesuvius. M. L. 

 Palmier! first observed at the distance of a few 

 hundred yards the flashes of volcanic lightning 

 from a new crater of Vesuvius, at Torre del 

 Greco. These flashes appeared always to ori- 

 ginate in large globes of smoke, and they were 

 followed by explosions not louder than the re- 

 ports of pistols. Afterward, from the observa- 

 tory he noticed similar flashes between smoke 

 and cinder masses below and bodies of aqueous 

 vapor above these ; but very seldom between 

 the smoke masses and the earth beneath. At 

 each violent projection of smoke, his instru- 

 ments indicated a strong tension of positive 

 electricity; and when this reached a certain 

 force, lightning and thunder occurred. If the 

 electric discharge occurred in the direction of 

 the zenith of the place, a sudden increase of 



positive electric tension was the result; while, 

 if the discharge was directed toward the earth, 

 or to a distant region of the air, the* tension 

 became negative. The vapor which moved to- 

 ward the observatory, if free from cinders, was 

 strongly positive; but the cinders which fell 

 when the smoke of a superior current deviated 

 from the zenith were negative. 



II. APPLICATIONS. Ritchie's Electrical Ma- 

 chines. The principle of induction .holds true 

 for current as well as for common electricity ; 

 illustrations being found in the facts that if 

 a wire or coil be made to transmit a gal- 

 vanic current while another wire or coil is 

 situated in immediate relation with this, but 

 not so as directly to receive the electricity 

 from it, and if along the first wire or coil an 

 interrupted or periodically reversed current be 

 transmitted, then at every such interruption 

 and recommencement, or reversal, of the pri- 

 mary current, a secondary or induced current 

 will be developed in the second wire or coil ; 

 and this induced current will partake in a large 

 degree of the properties of common electricity, 

 having great intensity, and being capable of 

 discharging itself to a corresponding distance 

 through dry air or other non-conductor a 

 power of which the primary or inducing cur- 

 rent is wholly destitute. If, further, the elec- 

 trical condenser be added at the extremity of 

 the second wire, so as to intensify the charge 

 arising in it at the moments of interruption, 

 the intensity and mechanical effect of the in- 

 duced current are still further increased. These 

 principles were determined by the researches 

 of Faraday, Ilenry, De la Rive, Fizeau, and 

 others. 



M. Euhmkorff, of Paris, was the first to pro- 

 duce an actual combination or machine repre- 

 senting and taking advantage of these prin- 

 ciples. This machine, known as Ruhmkorff's 

 induction coil, consisted essentially of an inner 

 helix of shorter and larger copper wire trans- 

 mitting a current from a galvanic battery, with 

 the addition of an interrupter to break the cur- 

 rent at regular intervals, this helix being sur- 

 rounded by and insulated from a second of finer 

 wire and much longer, having at one end the 

 condensing plates, and the extremities of which 

 constituted the poles of the secondary current. 

 With his arrangement the longest spark obtain- 

 ed did not quite equal one inch in length. Mr. 

 Hearder, in 1857, improved the apparatus by 

 more carefully insulating the helices, and ob- 

 tained sparks of 3, and subsequently of 6 or 7 

 inches. 



Mr. E. S. Ritchie, of Boston, Mass., desiring 

 in the same year to produce the induction coil 

 and of increased power, found it impossible to 

 construct it in the ordinary manner and yet 

 free from liability of the breaking through of 

 the spark from one coil to the other a casualty 

 that at once destroyed the action of the ma- 

 chine. His experiments led him to adopt an 

 entirely new plan of winding the exterior coil, 

 consisting finally in winding this wire in planes 



