WESTERN PARTS of PENNSYLVANIA. 225 



the lake extremely pleafant during the heat of the fiimmer 

 months, and have rrioft probably a very falutary influence 

 upon the atmofphere. 



A ftrong eafterly wind will occafion a confiderable 

 depreffion, and a ftrong wefterly wind a confiderable 

 fvvell of the waters in Prefqu' Ifle Bay. In the former 

 cafe, a portion of the water is driven towards the upper 

 end, and in the latter, towards the lower end of the lake. 

 To thefe caufes we are to attribute thofe ebbings, and 

 flowings, which have fo frequently been miftaken for 

 regular tides : for a little refle£lion will convince one, 

 that the moon can have no fenfible efFe£t upon the waters 

 of the lakes. When the wind ceafes the waters return to 

 reflore the equilibrium, and an undulation will be vilible 

 for feveral days after thofe ftorms, and appears to be but 

 flightly affedted by the alternate breezes already men- 

 tioned. 



In the weftern country, and efpecially in the neigh- 

 bourhood of the lakes, dews are very heavy. On the 

 Ohio and Allegany rivers, and their numerous branches, 

 fogs are very common, and of remarkable denfity ; they 

 do not however appear to contain any portion of thofe 

 noxious miafmata, which are fo frequently combined with 

 the fogs on the eaftern fide of the mountains ; nay the 

 inhabitants of Fittfburgh confider them as poffeffed of falu- 

 brious qualities. From a variety of obfervations 1 am 

 convinced that the atmofphere in the weftern country, 

 and particularly in the vicinity of the lakes, contains a 

 greater quantity of moifture than in the middle Atlantic 

 ftates. The wooden works which contained my inftru- 

 ments were always uncommonly fwelled, and frequently 

 very much injured in that country, though conftantly 

 defended from the rain, and occaf onally expofed to the 

 fun. The ivory and wood of my fedlors with brafs joints, 

 always expanded above the metal ; this expansion was 



not 



