570 



THE POPULAR SCIENCE MONTHLY. 



my researches from the rainfall question to this more general problem ; 

 and, with the intention of not being misled by local observations made 

 in the city itself, which, as we have just remarked, are not altogether to 

 be trusted, I have resorted to data of a more general topographical 

 kind, such, for instance, as the times of closing and opening of the 

 Hudson River. Also, with a view of extending the conclusions, what- 

 ever they might prove to be, to the Atlantic coast generally, I have 

 used such published records of the meteorology of Philadelphia, Bos- 

 ton, and Charleston, as I could find access to. These reach from 

 1738, with certain breaks, up to the present time. 



TABLE SHOWING- THE NUMBER OF DATS TIIAT TIIE HUDSON RIVER HAS BEEN 



CLOSED BY ICE. 



The data connected with the Hudson River have been derived from 

 the Annual Reports of the Regents of the University ; those of tem- 

 perature for the locality of New York itself, from the observations 

 taken at Fort Columbus, and by Prof. Morris, for the Smithsonian 

 Institution. The remainder are from the records of this observatory. 

 In the case of other Atlantic cities, the data are chiefly derived from 

 the reports of the United States Army officers to the Secretary of War. 



It appears from this that, from 1816 to the present time, we have 

 an unbroken register. Taking 1817 as our starting-point, we have to 

 1868 five periods of ten years each. The number of days during 

 which the river was closed in each of these five periods is : For the 

 first, 92 days; second, 92; third, 94; fourth, 90; fifth, 91. 



The third period gives a greater number of days than any of the 

 others ; the general mean is about 91 days. 



The conclusion at which we arrive from the evidence thus furnished 

 by the Hudson River is, that during 50 years, that is to say, the whole 

 period of trustworthy records, there has been no important change in 

 the number of days that the river has remained frozen. In this re- 

 spect the conclusion is the same as that which we have seen in the 

 case of the Baltic rivers for a period of 300 years. 



The evidence thus furnished from the closure of a river by ice 

 differs from that of thermometric observations. The latter give 

 merely the intensity of heat at the special moment, and in the special 



