366 Mr. C. Toralinson on the Motion of 



was no deposit whatever. The bottle was now wiped dry and 

 put in the angle of the window on which the sun was shining. 

 A thermometer placed near it marked 70° and rose to 78°. In 

 less than 25 minutes there was a copious deposit of small crystals 

 on the side nearest the sun. The warm woodwork prevented a 

 deposit on the furthest side : in fact the deposit was formed on 

 the side of the bottle where radiation was most free, even though 

 that side was most exposed to the sun. 



The result of this experiment was quite satisfactory to my 

 mind ; but as it is my duty to try and convince the minds 

 of other men, I may be allowed to pile up a few of these 

 proofs. 



When the surface of the earth and the air resting upon it are 

 of the same temperature, no dew is formed. If the earth be 

 cooled ever so little, there is condensation : so also if the 

 camphor bottle be surrounded by a medium of the same tempe- 

 rature, there is no deposit. Let that medium be of unequal 

 temperature, and a deposit is immediately formed on the colder 

 side. For example : a bottle containing crude camphor, which 

 had been kept in a cupboard during some months without showing 

 any sign of deposit (even when examined by that most delicate of 

 all tests, a lighted candle), was taken out, and a circular piece of 

 filtering paper of about the size of a florin was wetted with sul- 

 phuric ether, and so stuck on the outside of the bottle. { |In a few 

 seconds an abundant deposit was made on the inside, exactly cor- 

 responding with the external plaister. The experiment was re- 

 peated with paper dipped in alcohol, bisulphide of carbon, &c, 

 with the same result. I could now explain a result which had 

 puzzled me not a little. Bottles containing crude camphor were 

 from time to time placed on a shelf in a glazed bookcase close to 

 the door and opposite a window, and were occasionally changed 

 during several months. They were exposed to the diffused light 

 of the room, and formed furthest deposits during March, April, 

 and May, and no deposits at all during June, July, and August. 

 Now, during the first three months the room had a fire in it ; the 

 wall formed the back of the bookcase, and glass doors its front ; 

 consequently the back part of the bottles would feel the stream 

 of cold air from the door which passed along the wall to the 

 fire, while the front of the bottles, protected by the glass and 

 looking into the warm room, would preserve a higher tempera- 

 ture than the back ; and hence deposits were formed at the back, 

 and none in the front. When, however, fires were left off, the 

 stream of cold air from the door would cease to flow, the inside 

 of the bookcase would not vary in temperature, and the bottles, 

 being protected from radiation, would not be in a condition to 

 form deposits. 



