56B FOURTH REPORT 1834. 



from behind being directed upwards, to supply the spaces 

 above. The author states that the phaenomena of tropical and 

 other extraordinary rains and winds agree with the results 

 which may be deduced from the foregoing facts and consi- 

 derations. 



4. Origin of hail. — Referring to Sir J. Leslie's experiments, 

 and to the well-known effects of the compressed air in the 

 engine at Chemnitz, the author explains the formation of hail 

 by stating, that when very sudden and violent falls of rain take 

 place, especially in summer, the air, expanding into the void 

 space left aloft, robs the succeeding rain so effectually of its 

 caloric as to freeze the drops. The author proposes to pub- 

 lish his views in an enlarged form, with adequate illustration 

 by statements of obsei'ved facts. 



Extract of a Letter to Professor Forbes from Professor 

 Christie. 



The writer observed a very peculiar and well-defined light 

 proceeding, in the form of a ray, from the sun as it was setting, 

 having the sun for its base, and retaining the same position for 

 about half an hour. The ray was absolutely vertical, gradually 

 decreasing in splendour, until it was lost, at about the height 

 of 20° or 25° above the horizon, expanding but slightly from 

 its base to this point, and it was unaccompanied by any lateral 

 rays. Its expansion in breadth did not in any part exceed a 

 degree and a half on each side. These circumstances atti'acted 

 his attention on the occasion of his first witnessing the appear- 

 ance ; and on a more particular examination he was persuaded 

 that it could not be of the ordinary description of rays, pro- 

 ceeding from an opening in amass of cloud. Independently of 

 its permanence in a very peculiar position, there were appear- 

 ances in the ray itself which precluded such an opinion. The 

 SOth of June, the day on which he first observed the phaeno- 

 menon, had been clear and hot. At the time of the observa- 

 tion, above the sun there were faint streaks of haze, scarcely 

 to be denominated cloud, increasing in density towards the 

 horizon, and on these the ray was exhibited ; but he does not 

 remember to have noticed any well-defined clouds, even in the 

 horizon. At sunset on the 17th of July he again witnessed this 

 phaenomenon, but the ray was stronger and better defined than 

 on the former occasion, and although of much greater extent, 

 reminded him of the form and appearance of the tail of the 

 comet of 1819. Its position was, as before, absolutely vertical, 

 and it continued visible for about half an hour. The sky had 



