104- Dr. A. Waller's Observations on certain 



are very beautiful*. I have applied this property to the con- 

 struction of an instrument for measuring the chemical rays of 

 light. As the details respecting this would be foreign to our 

 present subject, I will defer them to another occasion, and con- 

 fine myself now to prove that these phamomena are indepen- 

 dent of the deposits caused by radiation. 



1st. The crystals are formed on the side exposed to the ac- 

 tion of direct or diffused light. 



2nd. They are not formed during the night, when the ra- 

 diation from the earth is sufficient to cause the deposition of 

 water. 



3rd. Green glass, which retards photographic action, like- 

 wise impedes this deposit. 



In an experiment which is now going on, a bottle of pale 

 green common glass is exposed to the north, while another of 

 white glass is placed in a southern aspect. The first became 

 covered with minute crystals, in size averaging about a milli- 

 metre, which have remained stationary for a week ; the second 

 is covered with arborescent ramifications, which are daily in- 

 creasing. 



Several familiar, but hitherto unexplained phaenomena, 

 may in my opinion be easily accounted for by these molecular 

 actions. 



The formation of hail I consider to be an instance of an 

 action precisely similar to that which causes the deposition of 

 the solids of gaseous and liquid particles. If we admit the in- 

 fluence of this force on the globular vapours of water, it is not 

 at all improbable that certain conditions may arise in nature 

 when these vapours may be much more liable to this influence 

 than we find them in our imperfect experiments. We have 

 seen that a solution of sulphate of soda or water in a pure 

 state may be brought by the abstraction of caloric to such a 

 condition of unstable equilibrium, that the slightest perturba- 

 ting cause will immediately reduce them to a solid form. 



If we admit that the globules which form the clouds are ca- 

 pable of being placed in a similar condition, we have sufficient 

 data to explain all the phaenomena that occur in the produc- 

 tion of hail. Any nucleus formed within a cloud in this state, 

 would create around it a deposition of all the neighbouring 

 particles; and the size of the hail-stones would be dependent 

 upon the thickness of the cloud it had to traverse. In the 

 storm at Ordenburg, in 1825, mentioned by Dr. Eversman, 

 pyrites was found in the centre, and had acted like a nucleus 



* I am informed by a friend, that this action of camphor was mentioned 

 twenty years since by Dr. Hope in his lectures, but I am not aware of any- 

 thing having been published upon the subject. 



