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



verts the whole water into a solid ma&s of ice. The pheno- 

 menon did not seem to have attracted any attention in this 

 quarter; and the facts which I stated, and the speculations 

 which I advanced, seemed to excite some surprise : the ice in 

 question, however, is perfectly famiUar to every person in this 

 country, though I never had seen any attempt to account for 

 its formation, and had long puzzled myself in vain to form any 

 plausible theory on the subject. 1 was not ashamed to confess 

 this at the time, and I expressly declared that 'the theory which 

 I proposed was intended to elicit, rather than impart, informa- 

 tion, and especially to direct attention to the alleged facts which 

 had been com^municated to me, and on which I founded my ex- 

 planation of the process. 



This kind of ice is well known in all northern climates, from 

 its annoying effects in obstructing all works which are carried 

 on by the impelling power of water. When ice collects on the 

 surface of mill-leads it is easily managed : it needs only to be 

 broken and floated down the stream : but when the ice of which 

 I am speaking forms, the case is perfectly hopeless ; the leads 

 are gorged up from the very bottom, and it is in vain to at- 

 tempt to remove the obstruction. This kind of ice is called in 

 Germany grund eis ; in France it is known by the name of 

 glace dejbnd ; and in the south of Scotland, it is called lappered 

 ice, an epithet which the common people apply to the natural 

 coagulation of milk. I am happy, however, that the pheno- 

 menon has now attracted the attention of some eminent philo- 

 sophers, particularly of the celebrated Arago in France, who 

 has been at great pains in collecting a variety of facts, and has 

 proposed a theory for the explanation of the appearance, which 

 I shall shew to be utterly inadequate for the purpose; and 

 which, with the modesty that characterises genuine philosophy, 

 he admits does not thoroughly satisfy himself. 



I beg leave to call the attention of the meeting, for a moment, 

 to the phenomenon itself. Every inhabitant of Perth who has 

 witnessed the setting in of a severe frost, must have observed 

 that before the true ice, as I may call it, has made much pro- 

 gress in advancing from the sides to the centre of the river, 

 nearly the whole body of the stream above the bridge is oc- 

 cupied by large irregular masses of floating ice of very consider- 



