42 



Prof. J. Prestwich. 



Artesian Wells in which there is an abundant overflow of Water at 



the Surface. 



48a 

 32 



31 

 lOl 



65 

 1S2 



34 

 144a 



Piace. 



Paris, St. Ouen 

 LiUe 



Tours 



Eochef ort 



Mondorff 



Minden 



Neu Salzwerk . 

 St. Petersburg. 



Strata. 



Tertiary 



Cretaceous ; Carbo- 

 niferous limestone 



Cretaceous 



Trias 



Lias and Trias . . . 



Triassic (?) 



Liassic and Triassic 

 Silurian 



Depth 



feet. 

 216 



329 

 460 

 2812 

 1647 

 2230 

 2038 

 656 



Temperature. 



At depth 



Fahr. 

 55 -3° 



57-2 

 63 5 

 111 

 78-3 

 90-9 

 88-3 

 54 



Mean 

 surface. 



Fabr. 

 51° 



50-5 



53 



54 '5 

 47 '3 

 48 

 48 



39 '17 



Bate 

 of 

 increase 



per 

 1° Pahr. 



feet, 

 50 



49 

 44 

 50 

 53 

 52 

 50- 

 44 



Mean.. 49 '1 



We thus have in these wells an average rate of increase of 49 feet 

 for each degree P., or if we take the mean of the two lists, of 

 almost exactly 50 feet per degree. Before, however, accepting this 

 conclusion, two points should be reserved for correction hereafter, 

 namely : 1st, the determination of the precise temperature at a depth 

 where the annual surface changes cease to be felt. 2nd, whether 

 there is any loss of heat, and what the amount, by the water in 

 ascending through the tubes. This latter is, I believe, not an unim- 

 portant consideration. 



The experiments at Grenelle indicate the probability of some such 

 loss, and the form of construction of the tubes gives strength to the 

 supposition. If the tubes of an artesian well were of the same diameter 

 throughout, the passage of any given portion of the water from the depth 

 to the surface would be direct, and the velocity the same throughout ; 

 but the tubes in almost all these wells decrease in diameter from the top 

 to the bottom, consequently, instead of the whole body of water being 

 in continuous and uniform motion throughout the length of the tube, 

 the velocity of the water gradually decreases from the bottom to the 

 top, currents are established at the points where the tubes enlarge, 

 and a certain time beyond that required for its direct trajectory must 

 elapse before the whole of the water issues at the surface. 



For example, at Grenelle, where the difference between the size of 

 the tubes at the top and bottom of the bore-hole is less than in some 

 wells, there are four tubes of the respective diameters of 0'25m., 

 0"22 m., 018 m., and 017 m. As the lesser the depth of the well the 



