Blodget.] lob [Feb. 21, 



THE NON- PERIODIC DISTRIBUTION OF HEAT IN THE 

 ATMOSPHERE. 



By Lorin Blodget. 



{Read before the American Philosophical Society, February 21, 1873.) 



The time has at length arrived when we can with some probability of 

 success, open the inquiry as to the causes of the remarkable facts of the 

 Non-Periodic distribution of heat in the atmosphere of the temperate 

 climates ; the necessary basis of observed facts being afforded in the 

 extensive series of means of temperature published in various works, 

 chiefly the War Department volumes ; and in the recent and most valu- 

 able system of the Signal Service. 



These extreme non-periodic changes are very remarkable on both sides, 

 that is, those of excessive heat in summer, and those of excessive cold in 

 winter, or in the colder months, since they often occur in other than the 

 technical winter months. So great are the consequences in simply the 

 sanitary point of view, that the National Health Association recently 

 formed, has made them the specific subject of inquiry : and at New York 

 the highly intelligent direction of the Health Commissioners has been 

 directed toward the introduction of special protective measures of a local 

 character to avert the fearful mortality which these periods of excessive 

 heat cause in that city. 



In a practical point of view the most urgent desire exists to ascertain 

 whetherthese excesses, especially of heat, can be indicated or foreshadowed 

 by telegraphic or other agency ; whether warning can be given, and care 

 for the preservation of life enjoined. In the extreme Northwest the 

 destruction of life from violent cold is as great as that in New York from 

 extra-tropical heat ; and admirable as many features of the present Signal 

 Service are, it does not at present give us any efficient action on the 

 specific point of preparing us for either of these extremes. 



In a philosephical point of view the inquiry is broader and more com- 

 prehensive. It is a great enlargement of the inquiry in regard to storms, 

 introducing new elements and more important calculations. It appears 

 to be broader in its scope than even the atmospheric circulation which 

 is now so well established, and through which most of the phenomena of 

 the evaporation and precipitation of atmospheric moisture are regularly 

 ordered and instituted. Storms are but incidents of this system of cir- 

 culation, with its consequences of evaporation in the tropics, and precipi- 

 tation in the temperate latitudes. We can set bounds to it, and fix its 

 constants with a fair degree of accuracy. The atmospheric movements, 

 whether superficial, or in the superior strata, can easily be reduced to a 

 resultant, and their significance determined almost as positively at the 

 40th parallel, as can that of the trade winds on the borders of the tropics. 

 The constants of atmospheric precipitation are also of comparatively 

 easy determination, and the sea of water falling in rain and snow can be 

 measured and its depth determined with a close approximation to accu- 



