406 METEOROLOGICAL CORRESPONDENCE. 



Fro7n James Balfour, Newport, Illinois. 



September, 1858. 



The remarkably mild winter in the months of January and December has 

 been sufficiently commented upon by the newspapers, but we cannot look to 

 them for the cause. The west and southwest winds prevailed nearly all the 

 time, especially in the upper atmosphere, very seldom changing to south or 

 northwest. It is well known that changes in the weather are produced by the 

 difference of temperature of the equatorial and polar currents. When two cur- 

 rents in different directions meet, clouds are invariably formed. When two cur- 

 rents unite in the same direction the sky becomes clear. On tbe 1st of Febru- 

 ary I had an opportunity of noticing three different currents in the air at the 

 same time. In the lower atmosphere the wind came from the north ; an east 

 wind drove light cirri from Lake Michigan, and above them were transparent 

 cirri coming from the southwest. Towards noon the two lower currents com- 

 bined in one, having a northeast direction, which, gradually veering to north- 

 west, ended in a snow-storm towards night, lasting till noon of next day. 



On the 3d a west wind made a clear sky, with the thermometer at 10° Fah- 

 renheit. 



On the 10th of February we had a temperature of 12° Fahrenheit; on the 

 11th, 18° Fahrenheit, with a shai-p west wind, whereby Lake Michigan showed 

 ihe phenomena of rapid evaporation, the whole expanse of water appearing like 

 a boiling caldron, light cirri over the lake indicating the transformation of 

 vapors into clouds. 



Rkmarks. — It cannot be doubted that on the meeting of the contiguous sur- 

 faces of two streams of air moving in opposite directions, and having different 

 temperatures, clouds must be formed, though I think it more probable that, in 

 accordance with the theory of the late Mr. Espy, rains and violent winds 

 are gen(u-ally produced by an upward motion of the air, and the inblowing from 

 opposite directions of currents of air to supply the ascending mass. 



The phenomenon mentioned by our observer, of the fog on the lakes, is an 

 interesting illustration of one of the ways in which fog is produced. While the 

 atmosphere was at a temperature of 18°, very nearly, if not entirely, all of the 

 vapor which it had contained was condensed, and it might be considered at that 

 temperature as incapable of holding any moisture. At the same time, since the 

 lake was not frozen, it had probably a temperature of about 40°, and would at 

 this temperature give off a considerable quantity of vapor, when not resisted by 

 the vapor already in the atmosphere. But as soon as this vapor was projected 

 into the exceedingly cold stratum of air above the surface of the lake it was 

 condensed into minute globules of water, constituting the elements of the cloud. 

 Paradoxical as it may appear, it is probable that more water was evaporated 

 from the surface of the lake during this extremely cold weather than was given 

 off on warmer days, when the air was more nearly saturated with vapor. lu 

 the case under consideration had the air been of the same temperature as that 

 of the water, or even greater, and fully saturated with moisture, no evaporation 

 would have taken place ; the vapor already in the atmosphere would by its re- 

 action prevented any more from being formed. 



From Geo. C. Huntington, Kellcy's island, Lake Erie, Ohio. 



May, 1859. 

 There is one feature in our climate which is peculiar. Dew during the heat 

 of summer is the exception, not the rule. This I know from observation con- 

 tinued ihrough twenty years' residence here. 



