Proceedings of' the Royal Society, 423 



at the expense of the British Association. They are still continued, 

 and the present notice contains only a first approximation to the 

 solution of the problems which th^y are intended to give. 



The chief aim of the experiments is to ascertain the progress of 

 Solar Heat in the Crust of the Globe, and has no immediate refer- 

 ence to the question of central heat ; the depth to which the expe- 

 riments extend being inadequate to aiford decisive results on that 

 head. 



The experiments differ in their object from any hitherto made, 

 from having an especial regard to the structure of the soil and the 

 conducting power for heat of different geological formations. With 

 this view three series of thermometers were constructed by Mr 

 Adie, under Mr Forbes's directions, each nearly of the same length 

 and range, and these were sunk in holes prepared for them to pre- 

 cisely similar depths, (1.) in the Trap Tufa of the Calton Hill, with- 

 in the Observatory grounds ; (2.) in the homogeneous bed of Sand 

 at the Experimental Garden ; and (3.) in the compact Coal Forma- 

 tion Sandstone of Craigleith Quarry, all in the immediate neigh- 

 bourhood of Edinburgh, and within a radius of about a mile. With 

 a view to render these observations more immediately comparable 

 with those made at Paris and Brussels, the extreme depth was the 

 same, or the lowest thermometer had its bulb at the distance of 

 24 French feet (= 25.6 English) below the surface, and the others 

 were placed at each station at depths of 12, 6, and 3 French feet.* 



The tube which connected the bulb with the reading part above 

 ground was made capillary, so as to contain as little liquid (alcohol) 

 as possible. Notwithstanding, all the observations have been ri- 

 gorously corrected for the inequality of temperature of their stems, 

 and likewise for the expansion of the liquid above ground. The 

 observations were commenced in February 1837, and have been 

 made once every week since. After being corrected they were 

 projected in the form of Curves : and the general consistency of 

 these with one another, and the peculiarities proper to each station, 

 are such as to give considerable confidence even in the first ap- 

 proximation, which extends from February 1837 to February 1838. 

 I. The general form of the curves at all the stations correspond- 



* At the Observatory a thermo-electric pair of iron and copper wires 

 was sunk along with the deepest thermometer, with a view to test the ap- 

 plicability of M. Peltier's apparatus to this object. Several observations 

 closely agreeing with the thermometer have thus been made. 



