168 ANNUAL OF SCIENTIFIC DISCOVERY. 



miles. In experimenting upon this point they had to consider : First, the 

 diminution of the current's power to produce mechanical effects ; and, 

 Second, its loss of speed. A voltaic battery of seventy-two pairs of plates, 

 each with a surface of sixteen inches, was set to work, and it was ascertained 

 how many grains the current would raise in an instrument contrived for this 

 purpose, and called the Magneto-Electrometer, upon being transmitted 

 through a wire just long enough to effect the connection. The number of 

 grains lifted was 25,000. The experiment being repeated with the same 

 current through 200 miles of wire, the number of grains lifted was 10,650; 

 with 400 miles of wire it was 3,250; and with GOO miles it was 1,400. 

 Clearly the loss of mechanical power in this case was not diminished in so 

 large a ratio as had been supposed. In regard to loss of speed, nearly five 

 thousand observations were made, with wires varying in length from eighty- 

 three to one thousand and twenty miles, to determine its ratio ; and from 

 these it appeared that with a wire eighty-three miles long the transmission 

 was effected in .08 of a second ; with 166 miles in .14 of a second ; with 249 

 miles in .36 of a second; with 498 miles in .79 of a second ; and with 1,020 

 miles in 1.42 of a second. Taking eighty-three miles as the unit, there was 

 in these observations a series of distances employed, which would be repre- 

 sented by numbers 1, 2, 3, 6 and 12. Consequently, if the law of the 

 squares of distance had applied, the transmission through the thousand mile 

 length of wire should have been one hundred and forty-four times as slow 

 as through the eighty-three miles length, or in other words, it should have 

 required nearly twelve seconds for its completion. The result of a very 

 large number of direct experiments and observations, pretty well established 

 the fact, that the velocity of movement of a magneto-electric current, 

 through a gutta percha covered copper wire -of the size of sixteen gauge, is 

 300 miles in from one-twelfth to one-sixteenth of a second ; 600 miles in 

 from one-sixth to one-ninth of a second ; and 900 miles in from one-fifth to 

 one-fourth of a second. The scries of distances being represented by 1, 2, 

 3 the corresponding series representing velocity becomes one-quarter, one- 

 ninth, one-sixteenth, or thereabouts. With a wire 500 miles long, 350 dis- 

 tinct signals were attainable in a period which allowed of exactly 270 dis- 

 tinct signals, when a wire 1,020 miles long was used. 



But the extent of the conductor is obviously not the only element con- 

 cerned in the velocity of transmission, for wires of equal dimensions and of 

 like composition. The velocity varies with the strength or quantity of the 

 electrical current sent through any given wire. Seven small pieces of zinc 

 were prepared and covered entirely with sealing wax, fragments of copper 

 wire being attached to serve as copper plates. The sealing wax was then 

 chipped off just from the point of each, leaving a portion of the metal bare, 

 to the extent of scarcely the size of the letter o on this page. These zinc 

 plates having been put into seven small acid-charged cells, and so constituted 

 a voltaic battery, a receiving instrument was set printing by means of their 

 Lilliputian energies through 600 miles of wire. The printing instrument 

 performed its work with the utmost facility, but, by means of the recording 

 apparatus already described, it was proved that the current took nine-tenths 



