NATURAL PHILOSOPHY. 127 



velocity in copper wire of 288,000 miles per second, but a moment's 

 consideration will show that the two results are not inconsistent. 

 The wire used in the American experiments was of iron, and about 

 three millimetres in diameter, while Wheatstone's copper wire w T as 

 l.Tmil. in diameter. We have every reason for believing that the ve- 

 locity with which electricity is conducted varies with the conducting 

 power of the medium, and should therefore naturally anticipate that 

 this velocity would be found greater in copper than in iron, for the 

 conducting power of iron is less than eighteen hundredths of that of 

 copper at C. Moreover, Wheatstone used machine electricity of 

 the highest possible tension. 



Besides these results of Wheatstone and Gould, we may state that 

 Walker has found a velocity of from 16,000 to 19,000 miles per sec- 

 ond, Mitchel of 30,000 miles a second, and Fizeau and Gounelle, 

 by experiments made the present year, of 63,200 miles in an iron wire 

 4 millimetres in diameter, and of 110,000 miles in copper w r ire 2.5mil. 

 in thickness. The latter gentlemen also infer, that the two electrici- 

 ties are propagated with the same velocity, that the tension of the 

 electricity has no influence on the velocity, that the velocity does not 

 vary with the section of the conducting material, but only with its 

 nature, and then not in the ratio of the conductive power, and that the 

 discontinuous currents " experience a diffusion, in consequence of 

 which they occupy a space greater at the point of arrival than of de- 

 parture." 



It is proper to add, that Dr. Gould suggests that, after all, the velo- 

 city is different at different parts of the line, and there are some facts 

 which favor this suggestion. 



Prof. Bache, in communicating to the American Association at 

 Charleston Walker's results, referred to above, stated that one inter- 

 esting fact observed in making these experiments is, that the telegraph 

 line, when connected with a battery in action, propagates the hydro- 

 galvanic waves in either direction, without interference. As several 

 successive syllables of sound may set out in succession from the same 

 place, and be on their way at the same time to the listener at a dis- 

 tance, so, also, where the telegiaph line is long enough, several waves 

 may be on their way from the signal station, before the first one 

 reaches the receiving station. Two persons at a distance may pro- 

 nounce several syllables at the same time, and each hear those emitted 

 by the other. So, on a telegraph line of two or three thousand miles 

 in length, in the air, and the same in the ground, two operators may, 

 at the same instant, commence a series of several dots and lines, and 

 each receive the other's writing, though the waves have crossed each 

 other on the way. 



DYNAMIC PHENOMENA OF THE LEYDEN JAR. 



AT the meeting of the American Association at New Haven, Pro- 

 fessor Henry gave an account of his investigations of the discharge of 

 a Leyden jar. On this subject he had made several thousand experi- 

 ments. All the complex phenomena he had observed could be refer- 



