148 ANNUAL OF SCIENTIFIC DISCOVERT. 



roscope employed consisted of a cylinder of wood, one inch in diameter and 

 seven inches long, placed in the angle of a black box with the electric lamp 

 inside, so that three-fourths of the cylinder were external, and in the dark 

 chamber where the audience sat, and one-fourth was within the box, and in 

 the full power of the voltaic light. By proper mechanical arrangements this 

 cylinder could be revolved, and the part which was at one instant within, 

 rapidly brought to the outside, and observed by the audience. As the cylin- 

 der could be made to revolve 300 times in a second, and as the twentieth 

 part of a revolution was enongh to bring a sufficient portion of the cylinder 

 to the outside, it is evident that a phosphorescent effect which would last 

 only theg-Q^Tj or even the g-oVo^ f a second might be made apparent. All 

 escape of light between the moving cylinder and the box was prevented by 

 the use of properly attached black velvet. The cylinder was first supplied 

 with a surface of Becquerel's phosphori. The effect here was, that when by 

 rotation the part illuminated was brought outside the box, it was found phos- 

 phorescent. If the cylinder continued to rotate, it appeared equally lumin- 

 ous all over, and when the rotation ceased, or the lamp was extinguished, 

 the light gradually sank as the phosphorescence fell. Then a cylinder having 

 a surface of quinine or aesculin, was put into the apparatus. Whilst the cyl- 

 inder was still, it was dark outside; but when revolving with moderate ve- 

 locity it became luminous outside, ceasing to be so the moment the revolution 

 stopped. Here the fluorescence was evidently shown to occupy time, in- 

 deed, the full time of a revolution, and taking advantage of that, the 

 self-shining of the body was separated from its illumination within, and the 

 fluorescence made to assume the character of phosphorescence. Another 

 cylinder was covered with crystals of nitrate of uranium, a hot saturated 

 solution having been applied over it with a fine brush. The result was 

 beautiful. A moderate degree of revolution brought no light out of the 

 box, but with increased motion it began to appear at the edge. As the 

 rapidity became greater, the light spread over the cylinder, but it could not 

 be carried over the whole of its surface. It issued as a band of light where 

 the moving cylinder left the edge of the box, diminishing in intensity as 

 it went on, and looking like a bright flame, wrapping round half the cylin- 

 der. When the direction of revolution was reversed, this flame issued from 

 the other side, and when the motion of the cylinder was stopped, all the 

 phenomena of fluorescence or phosphorescence disappeared at once. The 

 wonderfully rapid manner in which the nitrate of uranium received the ac- 

 tion of the light within the box, and threw off its phosphorescence outside, 

 was beautifully shown. The electric light, even when the discharge is in 

 rarefied media, or as a feeble brush, emits a great abundance of those rays, 

 which produce the phenomena of fluorescence ; but then if these rays have 

 to pass through common glass, they are cut off, being absorbed and de- 

 stroyed, even when they are not expended in producing fluorescence or phos- 

 phorescence. Arrangements can, however, be made, in which the ach-anta- 

 geous circumstances can be turned to good account with such bodies as 

 Becquerel's phosphori, or uranium glass. If these be inclosed within glass 

 tubes having platinum wires at the extremities, and which are also exhausted 

 of air and hermetically sealed, then the discharges of a Ruhmkorff coil can 

 be continually sent over the phosphori, and the effects, both fluorescent and 

 phosphorescent, be beautifully shown. The first or immediate light of the 

 body is often of one color; whilst on the cessation of the discharge, the sec- 

 ond or deferred light is of another, and manv variations of the effects can 



