SB1 PHILOSOPHICAL TRANSACTIONS. [aNNO 176§. 



exposed again to the common light of the day, the experiments may be repeated 

 with the same success as before. This has frequently been done, with some dry 

 phosphorus in glass balls which have been hermetically sealed, about 4 years, 

 without the least injury to the phosphorus ; as it appears to be as good now as it 

 was at first. 



Exp. VII. Let one end of a bar of iron, of about an inch square, or a poker, 

 be made red hot, and laid horizontally in a darkened room, till by cooling it 

 ceases to shine, or is but barely visible. Then bring a little dry phosphorus, 

 which has been exposed to light in a glass ball hermetically sealed, as near the hot 

 iron as possible, by holding the ball in contact with it ; and the phosphorus, 

 though invisible before, will in a few seconds begin to shine; and will discharge 

 its light so very fast as to be entirely exhausted of it in less than a minute; and 

 then will shine no more by the same treatment, till after it has been exposed to 

 light again. By this heat, light received from a candle, or even from the moon, 

 may be seen several days after. And phosphorus that will afford no more light 

 by the heat of boiling water, will shine again by the heat of the iron. By this 

 heat also, phosphorus which had been kept in darkness more than 6 months, 

 was found to give a considerable degree of light. 



It was the opinion of the great Sir Isaac Newton, that the rays of light are 

 very small bodies emitted from shining substances, and not motion propagated 

 through a fluid medium ; for several reasons which he has given in his Optics. 

 Notwithstanding which, it has been urged since his time, that light is nothing 

 but a repellent fluid put into very violent vibrations. Now Mr. C. thinks it im- 

 possible, if light be nothing but motion propagated through a fluid medium, and 

 not particles emitted from the luminous body, to account for the phenomena in 

 the 5th, 6th, and 7th experiments. That a substance should either give light 

 or not, when its parts are agitated by the same degree of heat, according as it 

 has or has not been exposed to light, for a few seconds of time, more than 6 

 months before ; seems plainly to indicate a strong attraction between that sub- 

 stance and the particles of light; by which it keeps many of them, in the com- 

 mon heat of the air, a long time, if not always : for the light the phosphorus 

 gives by being heated to a certain degree appears to be caused by its throwing 

 off adventitious particles, and not by any of its own ; since its light will de- 

 crease and be entirely gone, before the phosphorus will be hot enough to shine 

 of itself, or to emit particles of light from its own body. 



A writer against the Newtonian doctrine of light is pressed with a great diffi- 

 culty, and asks, if it be possible that a particle can move so far as from the sun 

 to the earth, and not frequently impinge upon other particles, when, he says 

 every part of space must contain thousands of them ? But this difficulty will nearly 

 vanish, if a very small portion of timeUfc allowed, between the emission of every 

 particle and the next following in the same direction. Suppose, for instance, » 



