Radiation in determining the Site of Malaria* 273 



subtile poison, prevalent only in certain places, or over very 

 circumscribed situations. Upon considering the various cir- 

 cumstances under which these diseases are produced, and the 

 impossibility of any poison dispersed through the air from the 

 ground becoming partial in its operation, or always confined 

 to any particular district (when every wind must waft it away 

 from the spot of its emanation), unless some adventitious cir- 

 cumstance influences its operations, — I am induced not to sub- 

 scribe to the doctrine which teaches that they take place from 

 a specific or peculiar and locally acting effluvium. On the 

 contrar}', I think we shall find that most of the ordinary at- 

 mospheric impregnations will produce the diseases of Malaria, 

 when under certain peculiar circumstances they are liberated 

 from their combinations; diseases which will, no doubt, be 

 violent or not, according to the quantity or quality of the mat- 

 ters developed. 



The atmosphere, as is well known, retains every where 

 mingled with it variable proportions of aqueous vapour, mixed 

 probably with various effluvia arising from the action of the sun 

 upon the many substances on the surface of the earth. During a 

 bright day, therefore, the air over those portions of the ground 

 subjected to its influence becomes saturated with vapour, and 

 any reduction of temperature by radiation will always be ac- 

 companied by the deposition of moisture and the precipitation 

 of a portion of those subtile matters drawn up by the agency 

 of heat; whereas any diminution of sensible caloric, which 

 may ensue from a rush of cold air, may not be accompanied 

 with the same effects : for it very often happens that such cur- 

 rents have not nearly attained their maximum point with re- 

 spect to vapour, and therefore none of these things happen ; 

 or if they do, the deposits occur in the form of rain, far less 

 prejudicial than those chilly fogs produced by the radiation of 

 caloric from the earth. 



When we think of the important process of radiation, the 

 effects of which have excited the attention of philosophers, 

 especially diose connected with horticultural pursuits, it is ex- 

 traordinary that it should wholly have escaped them to pursue 

 their investigations into this curious subject, with reference to 

 the momentous matter of local salubrity ; for little doubt re- 

 mains upon my mind, that a well conducted series of experi- 

 ments instituted to discover the phaenomena resulting from the 

 radiation of heat into the heavens, in different situations and 

 over various surfaces and soils in several places at the same 

 time, would discover to us an important field well worthy of 

 research as connected with the health of mankind. 



I have already endeavoured to draw the attention of those 

 New Series. Vol. 4. No. 22. Oct. 1828. 2 N who 



