10t Dr. Ritchie on the Detonation of Oxygen and Hydrogen. 



was brought over the land, these light clouds thickened, and 

 united into one dense and dark one. 



In company with Mr. John Phillips, I noticed this for about 

 half an hour, and so far as we could judge, it continued after 

 evening fall. On the following day both Mr. H. Thomas, to 

 whom I am indebted for the accompanying sketch, and myself 

 observed similar appearances on the same spot, which forms 

 the western boundary of the bay, and over the Lizard Point 

 (c), which terminates it on the east. 



I have several times subsequently observed the like. 

 Mr. Harvey * has described similar phaenomena occurring 

 in the neighbourhood of Plymouth : in this part of the country 

 I believe they are by no means unfrequent. 



I have the honour to remain, 8rc. 

 Geological Society. Penzance, W. J. Hf.NWOOD. 



Dec. 4, 18.33. 



XXI. On the Mode of detonating a Mixture of Oxygen and. 

 Hydrogen by a Spark induced by a small horse shoe Mag- 

 net. By the Rev. William Ritchie, LL.D., F.R.S., $c. 



Professor of Natural and Experimental Philosophy in the 

 Royal Institution of Great Britain, and in the University of 

 Eon don. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



JN a paper read before the Royal Society nearly two years 



ago, I first described the method of obtaining a spark from 



a small magnet sufficient to detonate a mixture of oxygen and 



* Edinburgh Journal of Science, Jan. 1S29, First Series, vol. x. p. 148." 



