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XVni. — Account of some Experiments on the Temperature of the Earth at differenl 

 Depths, and in different Soils, near Edinburgh. By James D. Forbes, Esq., 

 F.R.S., Sec. R.S. Ed., &c. Corresponding Member of the Institute of France, 

 and Professor of Natural Philosophy in the University of Edinburgh. 



I. History of the Observations. 



The proper temperature of our globe is a question which, formerly aban- 

 doned to speculation and hypothesis, has only lately been made the subject of 

 du'ect experiment. Preliminary to it, and intimately connected with it, is an- 

 other inquiry of great interest, namely, What is the thermometric effect of the 

 whole solar heat which falls in a year on the surface of the globe ? How much is 

 transmitted to the interior? How much dissipated at the surface? To what 

 depth does the influence of the seasons extend, and in what manner is that in- 

 fluence modified at different depths ? It is impossible to say to how many curious 

 and important inquiries a solution of these preliminary questions may lead the 

 way ; and it is to them that our attention is at present to be confined. We shall 

 not speak, except incidentally, of the absolute heat of the interior of the globe ; 

 we shall only discuss the modifications of the solar heating influence near its 

 surface. 



This inquiry was perhaps first agitated by the illustrious Lambert, a ma- 

 thematical philosopher of Germany, who yields, in originality, in comprehensive- 

 ness of mind, and in the successful application of mathematics to a wide range of 

 important physical subjects, to very few of his contemporaries or successors. 

 His experiments were made by M. Ott, a merchant at Zurich, who had a conve- 

 nient garden for introducing the thermometers.* 



Having claimed for Lambert the first systematic inquiry on this subject (for 

 the previous essays of Mariotte and Hales could not lead to any exact conclu- 

 sions), I shall not trace the subsequent history of the problem, which is fidJy stated 

 in M. Quetelet's papers, in the Transactions of the Brussels Academy for 1836 

 and 1840, and in the Annales de V Observatoire de Bruxelles, tome iv. (1845). 

 Such observations were made by Herrenschneidee, at Strasbourg ; Muncke, at 

 Heidelberg ; by Leslie, at Raith, near Edinburgh ; by Arago, at Paris ; by Que- 

 telet, at Brussels ; and by Rudberg, at Upsala. As it does not appear, that, in 

 making or discussing these observations, regard has been had to the influence of 



* Lambert, Pyrometrie, 4to, 1779, page 356. 

 VOL. XVt. part II. 3 B 



