370 



On the Motion of Camphor towards the Light, 



July 27. 



Furthest. 



Time. 



Nearest. 





68^° 



69 



69 



8 A.M. 



9 

 10 



67r 



68 

 68 



Three or four lines 

 of scattered deposit 

 nearest the light. 



Here again is the fact that on this warm and bright 

 morning, when the heat and the light were abundant, the 

 deposits were insignificant. This is easily explained when it is 

 considered that, in consequence of open doors and windows, the 

 temperatures indoors and out are nearly the same. The condi- 

 tions required for the production of fine deposits are warmth to 

 raise the vapour, and cold on one side to condense it. A room 

 warmed by a fire, and cold air outside, are favourable to the 

 result, so that the camphor-bottles in the window in cold weather 

 are in a better position than in this warm equable temperature. 



It may be supposed that the position of the charge in the 

 bottle may have something to do with the motion of the deposit. 

 To settle this point, I prepared four 8-ounce phials of white 

 glass, and put 10 grains of crude camphor into each. In 

 bottle A the charge was in a heap at the back of the bottle, in 

 B in the front, in C at the left-hand side, and in D on the right. 

 The bottles were placed in the window, and fine deposits were 

 formed in all four cases on the side nearest the light ; only, in 

 B, C, and D, the deposit was connected with the charge in the 

 same way as smoke may be said to be connected with the fire 

 that produces it. In bottle A there was no such connexion, the 

 deposit being exactly in front, while the charge that supplied it 

 was behind, and no visible connexion between the two. 



There is another point which may require notice in these days, 

 when men's minds are so strongly impressed with the actinic 

 action of light. Dr. Draper says that light passed through a 

 solution of bichromate of potash so as not to blacken nitrate of 

 silver, produces an aphelion deposit in a bottle containing cam- 

 phor. This is a mere effect of the absorption of heat. I arranged 

 a number of flat-sided bottles in pairs, the bottle nearest the light 

 containing a coloured solution, and the bottle in contact with it 

 containing camphor. The narrow sides of the camphor-bottles 

 were made opake, so that the light which passed into them came 

 through the coloured solutions only. These observations were 

 extended over several months, and in every case the camphor pro- 

 duced furthest deposits ; and when the bottle was turned round 

 so as to make the furthest deposit a nearest one, it invariably 

 went over to the furthest side. I also enclosed a white glass 

 bottle containing camphor in a wooden box furnished with a 



