2 80 Scientific In telUgen ce. —Na tural Ph ifosopft y a 



many thousands of leagues long, before the result could be ex- 

 pressed in the fractions of a second. It being thu& impossible 

 to arrive at any result by direct experiment, the Professor had 

 to task his ingenuity that he might attain his object in some 

 other way. After many fruitless attempts, he availed himself 

 of the following expedient, which has already yielded many in- 

 teresting- results,.- and which he hopes still farther to improve, 

 and render practically useful. He placed a double metallic 

 mirror at the extremity of an axis of rotation, to which, by 

 means -of ''a large spinning-wheel, he could give an exceedingly 

 rapid motion. The musical tone produced by the vibration of 

 a card attached to the axis, supplied the number of revolutions* 

 A luminous point, seen by the reflection of the two faces of the 

 moving mirror, produced, in every semirevolution, two luminous 

 circles, proceeding in the opposite direction to the mirror. All 

 inequalities of the flame were made manifest by the circles ap- 

 pearing more or less distinct. By means of this arrangement,, 

 he discovered a series of luminous condensations and dilatations 

 in the flame of hydrogen, when it produced sound in passing 

 through a glass tube. He also observed that the electrical 

 aura, as manifested in erecting feathers, down, &c. was not a 

 continuous stream, but a rapid succession of very minute sparks. 

 He then took a wire half a mile long,, which he cut in the mid- 

 dle, and arranged each half in such a way, that both extremities 

 and the central ends were in a line parallel to the mirror, so that 

 the three sparks appeared on one straight line. As this sensa- 

 tion on the retina continued longer than the impression, instead 

 of seeing points, which the three sparks should have produced, 

 he observed three arcs of a circle, the origins of which should 

 commence on the same right line, if the transit at the three sec- 

 tions were instantaneous. He imparted a velocity of 800 revo- 

 lutions in a second to the mirror. Even at this degree of velo- 

 city, the origin of the first and third arcs continued on the same 

 right line, but the middle one was somewhat in advance or be- 

 hind the other two, according to the direction which was given 

 to the rotation. Here the Professor remarks, that this experi- 

 ment does not agree with the view that electricity is a single 

 fluid, entering: at the one end and issuing at the other, as Frank- 

 lin's theory requires. As the sparks at the two extremities are 

 always consentaneous, whilst that in the middle appears somewhat 



