CHAP, ii.] ARTESIAN WELLS. 47 



the more distant as their depth is greater. The water-bearing sand 

 does not show itself nearer than the plain of Langres. Along the 

 whole extent of the basin where this cropping up to the surface 

 takes place, the sand-beds receive the rains which filter and descend 

 through their whole depth, thus constituting a succession of im- 

 mense curved tubes in which the water is more and more com- 

 pressed. It is easily seen therefore that in boring a well at a point 

 where the altitude is lower than that of the surface which receives 

 the rain, the water will rise in the well and will spout out above the 

 ground as soon as the depth of the boring is sufficient to reach the 

 water. At Passy, the water rises, as shown in Fig. 26, to a very con- 

 siderable height, the delivery being not less than 17,000 cubic metres 

 in twenty-four hours. 



The process of boring, although it is in the present day greatly 

 improved, does not prevent serious difficulties being encountered, 

 when artesian wells have such great depth as those of the Paris basin 

 just mentioned. If the drills, the boring bits, or their rods (which 

 are the tools used to bore the rocks and draw up the debris to the 

 surface) happen to break, it often requires very long and expensive 

 operations to free them. 1 



V. THE PirETTE. THE MAGIC FUNNEL AND INEXHAUSTIBI 



We described, when dealing in the Forces of Nature with the 

 Syphon, an interesting and useful experiment, showing how the pres- 

 sure of air might be brought to bear on the flowing and decanting 

 of liquids. The pipette is a little instrument answering a similar 

 purpose. It allows us to draw into another vessel a portion of liquid 

 contained in a vessel which we are unwilling to disturb. It is a tube 

 with a tapering end of tin or glass; this is immersed in the liquid, 

 and is filled either by simple communication or by aspiration. 



Once full, the pipette is held as is shown in Fig. 27, by placing 

 the finger on the upper opening ; then on withdrawing it from the 

 vessel, the atmospheric pressure which is exercised on the liquid at 



1 For a detailed description of the boring of an artesian well, we must refer to 

 special works, among which is the Guide du Sondeur, by M. Degousee, and 

 L* Hydraulique, by M. Marzj? (Bill, dcs Merreilhs}. 



