170 Rev. Mr Eisdale's Observations on Ground-ice. 



part of the country, wrote me a letter containing a theory of his 

 own, ascribing the phenomenon to the prevalence of particular 

 winds; in confirmation of which he mentioned, that, during a 

 severe frost, when his mill-lead was entirely free of any kind of 

 ice, he had occasion one day to lop some branches from a tree 

 which overhung the lead ; one of them fell into the water and 

 was left there, as he did not apprehend any consequences from 

 such a trifling occurrence. Next day, however, to his astonish- 

 ment, the water was turned entirely out of the lead, and had 

 overflowed a large portion of an adjoining meadow. On pro- 

 ceeding to ascertain the cause, he found that a solid barrier of 

 ice had been formed across the lead where the branch had fallen 

 in, so as completely to prevent any water from passing, whilst 

 the rest of the lead was free from ice. He ascribes this to the 

 prevalence of a very sharp north-east wind which had blown 

 durinff the nifjht. There can be no doubt that this is convert- 

 ing into a cause, what is merely an accidental concomitant, as I 

 shall shew hereafter. 



On the 16th February 1827, M. Hugi, President of the So> 

 ciety of Natural History at Soleure, while standing on the 

 bridge of the Aar, and when the river was perfectly clear of ice, 

 observed in these circumstances, large icy tables continually 

 rising from the bottom of the river, in a vertical direction, and 

 with such buoyancy, as to rise considerably above the surface, 

 when they immediately sunk into a horizontal position, and 

 floated down the stream. A great many facts of the same kind 

 may be found in M. Arago's paper, which is given in the Edin- 

 burgh New Philosophical Journal for July last ; which is the 

 first paper on the subject of ground-ice that I have ever seen. 



Let us now attend for a httle to the cause of these singular 

 phenomena, and I will be bold to say that no adequate cause 

 has yet been assigned for them ; Unless the hints which I for- 

 merly threw out on the subject as queries, rather than as ascer- 

 tained facts, shall be considered sufficient for the purpose. M. 

 Arago gives his theory as to the cause at great length. It is 

 simply this, that the different strata of water, in a running and 

 shallow stream, being all mixed together by the agitation caused 

 by the inequalities of the bottom, are all cooled down during an 

 intense frost to the freezing point, and that the stones there 



