526 THE POPULAR SCIENCE MONTHLY. 



the air (which he hoped would moisten the powdered plaster suf- 

 ficiently to cause it to set firmly into whatever form it collected). 

 The jet was directed against a splinter of wood. 



In this way masses of plaster very closely resembling hailstones 

 were obtained. They were all more or less conical, w T ith their bases 

 facing the jet. But, as might be expected, the angles of the cones 

 were all smaller than those of the hailstones. Two of these figures are 

 shown in the sketches annexed. 



The strias were strongly marked, and exactly resembled those of 

 the hailstone. The bases also were rounded. They were somewhat 

 steeper than those of the hailstone; but this was clearly due to the 

 want of sufficient cohesive power on the part of the plaster. It was 

 not sufficiently wet. Owing to this cause also it was not possible to 

 preserve the lumps when they w T ere formed, as the least shake caused 

 them to tumble in pieces. 



Similar masses were also obtained by blowing the vapor of naph- 

 thaline, but these were also very fragile. Whereupon it is remarked : 

 At ordinary temperatures the powdered naphthaline does not adhere 

 like ice when pressed into a lump. No doubt at very low temperatures 

 ice would behave in the same way, that is to say, the particles would 

 not adhere from the force of impact. Hence it would seem probable 

 that, for hailstones to be formed, the temperature of the cloud must 

 not be much below the freezing-point. 



That the effect of the temperature of the cloud exercises great 

 influence on the character of the hailstones cannot be doubted. And 

 if, as has been suggested by M. L. Dufour, the particles will sometimes 

 remain fluid, even when the temperature is as low as Fahr., it is 

 clear that, as they are swept up by a falling stone, they may freeze 

 into homogeneous ice either in a laminated or crystalline form. 



The author then proceeds to show that raindrops are probably 

 formed in the same way as hailstones ; that, although the raindrops 

 have no structural peculiarities like the hailstones, the aggregation of 

 the particles of water by the descent of the drop through the cloud is 

 the only explanation which will account for them. He shows that, as 

 Mr. Baxendell had previously pointed out, the amount of vapor which 

 a cold drop could condense before it becomes as warm as the vapor 

 would be inappreciable when compared with the size of the drop; and 

 since, in order that there might be condensation, the air must be 

 warmer than the drop, the drop could not part with its heat to the 

 air. He also shows that during the time of descent of a large drop 

 the heat lost by radiation would not account for the condensation of 

 sufficient vapor to make any appreciable difference in the size of the 

 drop. Whereas, if we suppose all the vapor w T hich a body of saturated 

 air at G0 Fahr. would contain over and above what it w r ould contain 

 at 32 to be changed into a fog or cloud, then if a particle, after 

 commencing to descend, aggregated to itself all the water suspended 



