3 SO On the Dependence of Malaria on Terrestrial Radiation. 



the foregoing observations* if they shall be found correct, to- 

 wards the attainment of that desirable end, the protection of 

 mankind against the injurious impregnations of the air. 



As regards the prevention of the rise of miasms from the 

 ground, I fear we have too little controul over the powerful 

 agency of the rays of the sun to adopt successfully any plan 

 with reference to this head. The solar influence is too great and 

 too general to enable us to obstruct the emanation of various 

 effluvia from the soil : nevertheless, much may be done by re- 

 moving as far as possible from the surface of the ground any 

 thing likely to afford them ; and although our endeavours on 

 this point must be very inefficient, they may be more success- 

 ful and beneficial if directed to obviate those conditions which, 

 as we have seen, have such a considerable effect in rendering 

 active the noxious properties of malaria; viz. 1st, by prevent- 

 ing the dissipation of caloric through a still atmosphere; 

 and, 2ndly, by promoting those aerial currents which tend so 

 much to dilute and carry off any deposition which may ensue 

 from that process. 



In order to accomplish the former of these indications, we 

 must use every means in our power to diminish the radiation 

 of heat from the ground after sun set, or to remove as far as 

 possible from the circle of its operation, by attaining during 

 the night-season some moderate elevation, interspersed here 

 and there with lofty trees, and hedges or inclosures, and placed 

 to windward of the more rapidly radiating surfaces which may 

 be near : for although we speak of a calm and still atmosphere 

 as being highly favourable to the development of malaria, still 

 it must be understood that in almost every instance there are 

 gentle, although perhaps imperceptible currents in the air, fully 

 sufficient to waft to a considerable distance the miasms libe- 

 rated by the dissipation of caloric ; and any increase of tem- 

 perature which such currents may acquire in their passage over 

 less perfect radiators, will not always be enough to disarm them 

 of their injurious influence. In situations therefore more 

 particularly, where we are likely to be subjected to miasma- 

 tous products, and where the air at night is generally still, or 

 where the gentle breezes are found to sweep over tracts fa- 

 vourable to radiation, it behoves us to endeavour, — by exciting 

 artificially aerial currents, and by raising or keeping up the 

 temperature of the air of the place where we may be by cir- 

 cumstances constrained to remain, — to prevent the deposition 

 and development of malaria. This may be accomplished by 

 lighting large fires to windward of the place of our nightly so- 

 journ. — This is not a new idea: fires have already been observed 

 to be beneficial in warding off the nocent power of malaria, 



though 



