1823.] Sir H. Davy on the State of Water, fa. 43 



scarcely two places of equal depth below the surface, and under 

 similar circumstances, exhibit the same temperature. As these 

 differences and irregularities of temperature always occur in 

 mines which are at work, they must arise from adventitious 

 causes. I am, therefore, of opinion, that the true temperature 

 of any part of a mine in the full course of working is difficult of 

 attainment, and that we must have recourse to those mines, and 

 parts of mines, which have been long since quitted by the miner, 

 in order to obtain any thing like a true datum. 



The hot springs which frequently occur, while they prove the 

 existence of causes sufficient to give them their high decree of 

 temperature, prove, at the same time, by their rarity, the local 

 and adventitious nature of those causes. 



I cannot conclude without stating, that I hope those gentle- 

 men who have taken such an interest in the present inquiry, will 

 not lose sight of it, but avail themselves of every opportunity 

 likely to develope this apparently mysterious subject ; and as we 

 are in possession of the temperatures of Huel Ann, and the Her- 

 land mine, and which are to be immediately reworked, and of 

 Huel Abraham, our deepest mine, which report says is about to 

 be relinquished, I think a favourable opportunity will occur to 

 reverse the nature of our present experiments, and thus afford 

 by synthesis, as well as analysis, an accurate statement of 

 facts. I am, Sir, vour obedient servant, 



M. P. MoYLE. 



Article IV. 



On the State of Water and Aeriform Matter in Cavities found in 

 certain Crystals. By Sir Humphry Davy, Bart. PRS.* 



There are few inquiries in natural science more calculated to 

 awaken our curiosity, than those relating to the changes which 

 the matter composing the surface of our globe has undergone. 

 The imagination is excited by the magnitude of the operations 

 by the obscurity of the phenomena, and the remoteness of the 

 time at which they occurred ; and all the intellectual powers are 

 required to be brought into activity to find facts or analogies, or 

 to institute experiments, by which they may be referred to known 

 causes. 



The crystallizations constituting the whole of the rocks which 

 are usually called primary, and those found in such abundance, 

 even in the rocks which are termed secondary, prove that a 

 considerable part of the materials of the surface of the globe 



ft 



* From the Philosophical Transactions for 1822. Part II. 



