New York Weather Bureau. 443 



declines toward the north; Dr. Hann. having shown that the pre- 

 vailing air currents are generally less cooled when passing up a 

 gradual incline than when the vertical gradient is large. 



It has already been stated that the thermal influence of Lake 

 Erie is distinctly noticeable in the spring and autumn over the 

 large tract which slopes toward its surface; and that a difference 

 of about one degree is thus brought about between western 

 Wyoming icounty and adjacent stations in Allegany county. After 

 the freezing of Lake Erie, the coldest region of the plateau ap- 

 pears to be the ridge separating the system of the G-enesee river 

 vfrom that of Lake Erie. Lake Ontario, remaining open through- 

 out the year, can not fail to temper somewhat the winter climate 

 of the region as a whole. 



It may be noted that Humphrey, in central Cattaraugus county, 

 has a higher temperature than might be expected from its elevated 

 position and the character of the surrounding country. This sta- 

 tion belongs to the upper limit of the Ohio valley, and it seems 

 poisisible that special climatic conditions miay thus be introduced 

 here. iSoutherly winds are found to occur at Humphrey more fre- 

 quently that at adjacent stations to the northward; but whether 

 these belong to a general system, or are merely local^ must be 

 decided by further observation. 



The general equality of temperature over the eastern plateau 

 is rather remarkable when the extent and irregular surface of the 

 region' are eonsidered. The sea-level isothermis in the southea'stern 

 portion show the influence of the ocean to a small degree; but in 

 fact this effect is masked by the high altitude and mountainous 

 character of the section, excepting at Minnewiaska, which overlooks 

 the plains toward the southeast, and is fully expoised to air cur- 

 rents from that direction. Middletown, which occupies a sheltered 

 position still further southward, may for climatie purposes be 

 properly classed as a station of the Hudson valley^, to whose influ- 

 ence it is mainly subject. 



The narrow valleys of the highlands are found to vary but little 

 in average temperature from the adjacent hills; while in case of 

 the broader depresisions more heat is gained during the day than 



