278 



ELECTRICITY. 



18,000 men, as fixed by the firman of the Sul- 

 tan ; the second to the exclusive fortifications 

 on the coast, and other warlike preparations ; 

 the third to the oppressive taxes ; the fourth 

 to the Armstrong cannon which the Khedive, 

 in 1870, while giving up his iron-clad vessels, 

 had retained. In the fifth place, the Turkish Gov- 

 ernment demanded that the Khedive for sev- 

 eral weeks should receive on the isthmus a Turk- 

 ish force, the number of which was not speci- 

 fied. In his reply, the Khedive expressed a 

 strong wish to remain at peace with the Sul- 

 tan, and asserted that on most of the above 

 points the Turkish Government was misin- 

 formed ; the number of his troops was not 

 larger than was indispensably necessary for 

 maintaining public order; the fortifications 

 were necessary for the defence of the coast; 

 the new loans and taxes had become necessary 

 in consequence of the extensive public works. 

 With regard to the last Turkish demand, the 

 reply was evasive. 



Later in the year both Turkey and Egypt 

 showed a more peaceable disposition. The 

 Khedive in August sent his aunt to Constan- 

 tinople to assure the Sultan that her nephew 

 would strictly fulfil all his duties. The Porte, 

 on the other hand, deemed it best to disclaim 

 for the present any intention to reduce Egypt 

 to a condition of greater dependency than be- 

 fore. In October the Khedive, in compliance 

 with the wish expressed by the Turkish Gov- 

 ernment, considerably reduced the taxes, and 

 announced his purpose to consolidate the en- 

 tire floating debt. 



The session of the Egyptian Chamber of 

 Representatives was closed by the Khedive on 

 August 7th. The speech assured the repre- 

 sentatives that the propositions and sugges- 

 tions made by them had greatly pleased the 

 Government. The president of the Chamber 

 thanked the Khedive for the kind attention he 

 had given to their wishes, especially as regards 

 the new institution of the Interior. 



ELECTRICITY. Duration of the Electric 

 Sparlc. Prof. Ogden D. Rood makes a second 

 report to the American Journal of Science with 

 regard to his experiments to determine the 

 duration of the discharge of a Ley den jar, con- 

 nected with an induction coil. His first paper 

 on the subject was noticed in the ANNUAL 

 CYCLOPEDIA for 1869. The later experiments 

 were conducted with a jar having a coating of 

 11 square inches only, instead of about 114 

 square inches, used on the former occasions. 

 For the mirror he employed silvered glass, half 

 an inch square, the polished silver side reflect- 

 ing the light. The mirror was made to revolve 

 300 times in a second, the apparatus used be- 

 ing essentially like that introduced in the 

 former experiments. With zinc points and a 

 striking distance of 1 millimetre, the dura- 

 tion of the spark varied between .000001 and 

 .000025 of a second, a duration as long as 2^- 

 millionth^ of a second being somewhat rare. 

 With zinc points and a striking distance of 2 



millimetres, two careful experiments gave re- 

 spectively a duration of .0000022 and .0000019 

 of a second. Although with the improved 

 micrometric method, adopted by Prof. Rood, 

 an interval of time as small as one millionth 

 of a second could be directly measured, yet he 

 says he could never detect any sign that the 

 " duration of the great body of the spark was 

 other than absolutely instantaneous ; " as, how- 

 ever, all the light of the spark is due to incan- 

 descent particles, we must suppose that an in- 

 finitesimal portion of time is required for at- 

 taining its maximum brightness, and, owing 

 to the same reason, its disappearance demands 

 another distinct period of time, however 

 minute. With the mirror revolving 840 times 

 a second, and platinum points at a striking dis- 

 tance of 3 millimetres, the observed duration 

 of the discharge was .000000094. Prof. Rood 

 narrates. his further experiments with this dif- 

 ficult problem, as follows : 



Before finally abandoning the attempt to deter- 

 mine the actual duration oi the discharge, another 

 effort was made ; a second lamp-black plate was pre- 

 pared, in which the breadth of ^he image of a line, 

 black or white, on the observing plate was a 1 * of a 

 millimetre. These lines were viewed with the ter- 

 restrial eye-piece of a small telescope ; it enlarged 

 them ten diameters, and care was taken with all the 

 adjustments, so that a good clean image should be 

 produced. Platinum wires SB of an inch in diameter 

 were used, with a striking distance of five millimetres. 

 By gradually increasing the weight, it was proved 

 successively that the duration was less than eighty, 

 sixty-eight, fifty-nine, fifty-five billionths of a sec- 

 ond ; and, finally, the lines, after growing fainter and 

 fainter, entirely disappeared, giving as the result a 

 duration of forty-eight billionths of a second. In 

 a large number of observations I could detect no 

 discharge lasting during a smaller interval, though 

 the apparatus was now fully capable of making evi- 

 dent much smaller periods of time. 



When the striking distance was reduced to one 

 millimetre, the duration was shorter ; in the case of 

 of the sparks, the duration was slightly greater 

 than forty-one billionths of a second, the remaining 

 being slightly less than this figure. 



With a striking distance of three millimetres, the 

 duration was between forty- one and forty-eight bill- 

 ionths ; and, when the striking distance was in- 

 creased to ten millimetres, it was between forty- 

 eight and fifty-five billionths of a second. 



An effort was made to make a corresponding set of 

 measurements with brass balls instead of platinum 

 points ; and it would seem probable that the duration 

 of the discharge is somewhat increased by their use 

 (or that many of those with shorter durations are 

 suppressed). With brass balls not nearly so many 

 discharges take place in a given time as with points"; 

 hence, the work becomes tedious and less certain. 

 The evidence from twenty-six observations, gathered 

 in not less than three hours, went to show that the 

 duration, with a striking distance of five millimetres, 

 was between forty-eight and fifty-five billionths of a 

 second. 



It has thus been shown that the duration of the 

 first act of the electric discharge is in certain cases 

 only forty billionths of a second, an interval of time 

 just sufficient to enable a raj of light to travel over 

 forty feet. 



The author has succeeded with this ap- 

 paratus in measuring intervals as small as 

 .000000028; and he hopes to reduce that as 

 low as .000000010. 



