172 ON RAIN, ENAPORATION, 6lc. 



Wcftmorland, to be 20 miles in length, and the excefs 35 

 inches, the rain and dew being fuppofed 65, and evaporation 

 30 inches. 



20* x 35 x Q 7 Q 



Thcn ' SbTFlTi == 7ob~ = q <>r Q == 14* q ; which 



refult, I believe, will be found to accord nearly with the mea- 

 lureraent of the two rivers on the principle before mentioned. 



SECTION 4. 

 On the Origin of Springs. 



Orofe of fprings. The origin of fprings has always beenjuftly confidered as 

 a queftion of natural hiliory worthy of inveftigation. — In the 

 infancy of fcience hypothefes are formed to account for phe- 

 nomena ; but when facts are difcovered totally inconfiftent 

 with an hypothecs, it ought to be difcarded. This does not 

 feem to have been the cafe in the fubject before us ; for vari- 

 ous opinions are ftill held by fome, which it is impoffible to 

 fupport by fads. The object of the following remarks and 

 experiments is to afcertain the difputed point if poffible. 



Opinions. There are three opinions refpecling the origin of fprings 



which it may be proper to notice. 



i. Rain and 1ft. That they are fupplied entirely by rain and dew. 



dev ^* 2d. That they are principally fupplied by large fubterra- 



refervoirs. nean refervoirs of wates. 



3. Filtration 3d. That they derive their water originally from the fea, 



from the fea. on ^ pr i nc i p l e f filtration. 



Whether the It is obvious, that before we pay any attention to the two 



firft caufe be in- ] atter op i n i ons the caufes afiigned in the firfl ought to be 

 furacienr. ' r . ' ° . __ , . TT . 



proved lnlumcient by direct experiment. M. de la Hire is 



the only one who has attempted to do this, as far as my in- 



De la Hire's ex- formation extends, in the Parifian Memoirs for 1703. He 



Snfoaked ° P rocure d a leaden veffel eight feet deep, having a pipe at the 



through a mafs bottom ; this he buried in the earth, and filled with foil of 



of earth eight f anc j an d loam, expofing the furface to receive all the rain 

 xeet thick. r ° 



that fell. After 15 years trial, he found that no water had 



run through the pipe at the bottom. 

 Shallower veflel. Again, he took another veffel, eight inches deep, which he 

 filled with earth and expofed in like manner. No rain pene- 

 trated fo as to run out at the bottom from June to February ; 

 2 but 



