540 



arbitrary and, as the author conceives, entirely inadmissible hypo- 

 theses into the problem. 



For the purpose of testing this theory in its application to our 

 own globe, four or five cases of Artesian -wells and vertical shafts are 

 especially referred to, in which the temperature has been carefully 

 observed at greater depths than at any other places in Western 

 Europe, or probably in any other part of the globe*. The cases 

 spoken of are the following : 



(1) An Artesian well near Geneva. Depth = 225 metres; increase 

 of depth for 1 (F.) = 55 feet. 



(2) An Artesian well at Mondorff in the Grand Duchy of Luxem- 

 bourg. Depth = 730 metres; increase of depth for 1 (F.)=57 feet. 



(3) An Artesian well at New-Saltzwerk in "Westphalia. Depth 

 = 644-5 metres; increase of depth for 1 (F.)=54 feet. 



(4) The Puis de Crenelle at Paris. Depth =546 metres; increase 

 of depth for l(F.)=60feet. 



(5) A coal shaft at Duckenfield, near Manchester. Depth= 1400 

 feet ; increase of depth for 1 (F.)=65 feet. 



(6) A coal shaft at Monkwearmouth. Depth about 1/00 or 1800 

 feet; increase of depth for 1 (F.) about=60 feet. 



The general rate of increase of temperature in our own deeper 

 coal-mines is that of about 1 (F.) for 60 feet in depth; and the 

 same result has been obtained for many parts of the chalk in North- 

 ern France. 



These cases present a remarkable approximation to uniformity, 

 whereas the conductive powers of the strata which have been pene- 

 trated are very different. Cases (4) and (5) present the best means 

 of comparison. The Puis de Grenelle passes through nearly 500 

 metres of chalk, the conducting power of which is estimated by the 

 author at somewhat more than '25, while the mean conducting 

 power of the rocks through which the coal shaft at Duckenfield 

 passes, is estimated, by means of experiments performed on speci- 

 mens of these rocks, at rather more than '5. This is about twice as 

 much as in the former case, whereas the depths corresponding to the 

 same increase of temperature are only as 65 to 60, instead of being 

 in the ratio of about 65 to 35, as they ought to be according to the 



* tn a great majority of instances observations of this kind have not been 

 made with sufficient care to be relied on. 



