40 



Prof. J. Prestwich. 



between the surface and the well temperature), we get a quotient of 

 46'5, which agrees nearly with the thermometric gradient of the well 

 at St. Petersburg (No. 44). March, 1886.] 



Southampton. — The well was too long disused ; during that time 

 convection currents operated ; apparently no protection against con- 

 vection currents during the experiment. 



JSootle. — The influx of water at different levels, and convection 

 currents, render the results here valueless. 



Rouen, St. Sever. — The thermometer was not protected against 

 pressure, but-the effect of the pressure was estimated and allowed for. 



Troyes. — M. Walferdin thought it probable that the observations 

 were affected by the heat caused by the boring tools, sufficient time 

 not having been allowed to elapse after working before the thermo- 

 meter was sent down. 



Artesian Wells and Bore-holes in which the Water stood below the 

 Surface, or rose very slowly so as to render it necessary to take the 

 temperature at the bottom of the bore-hole. 



Original 

 number. 



Place. 



Strata. 



Depth. 



Temperature. 



Thermo- 

 metric 

 gradient. 



At depth. 



Mean 

 surface. 



129 

 231 

 3* 

 36 

 29 



209 



144 



Kentish Town 



Richmond. . . . 



Grenelle, Paris 



13 cole Mili taire, 

 Paris 



Sperenberg . . . 



Tertiary, Chalk, and 

 Old Red Sandstone 

 Tertiary, Chalk, Ju- 



Tertiary, Chalk, and 



Tertiary and Chalk. . 



Tertiary (Molasse) . . 

 Tertiary and Chalk. . 

 Triassic rock salt and 



feet. 



1100 



1337 



1312 

 568 



713 

 981 



E.ft. 



3490 



Fahr. 



69-9° 



75-5 



74-7 

 61 -5 



62-7 

 71-6 



115-5 



Fahr. 



49° 



49-6 



51 

 51 



47 

 50 



48-3 



feet. 



52-3 



51-5 



55 

 54 



48-5 

 45 



52 



Mean 



51 2 



Overflowing Artesian Wells. — We now come to surer ground. 

 Under certain conditions, these wells must give not only the nearest, 

 but a very near, measure of the underground temperature, at the level 

 from which the water rises. These conditions are — 



1st. A sufficient depth aud a sufficient distance of the out-crop of 

 the water-bearing strata from the point of overflow. In a case like 

 the Grenelle well, which is nearly 2000 feet deep, and where the 

 stratum which serves as a channel for the water does not come to the 



