Radiation in determining the Site of Malaria, 277 



rivers, millponds, &c." — " The meadow lands about Fontain- 

 bleau, at the junction of the Yonne and the Seine, are noto- 

 rious for the Jievre du pays; so injurious are they, that few 

 escape intermittents or remittents over a considerable tract." 

 If some great portions of the meadow-land in England have 

 been recovered by drainage from a state of marsh, and are 

 now as dry as the ordinary low-lands of plains and valleys ; 

 and if these localities still produce malaria and its conse- 

 quences, — it is another point of evidence against the salubrity 

 of meadows generally. " It is a rooted opinion in England, 

 that there can be no malaria on the banks of a running stream ; 

 and as far as mountain-torrents are concerned, this is probably 

 true : but where rivers slowly meander through low grounds, 

 we must not trust to the mere motion of the water." — " For 

 whatever persons may still think as to rivers in general in our 

 own country, there is no doubt that such streams as the Ouse, 

 the Lee, and all others flowing with difficulty through fertile 

 meadows, and with a flat vegetable margin, are productive of 

 malaria." 



But not to occupy more than necessary the time of the reader 

 by quoting further from Dr. Macculloch's Essay, I shall only 

 observe that this author has found small streams bordered 

 by thin and grassy margins; tranquil and stagnant waters, 

 especially in hot countries ; and ponds occupying but a small 

 space, — to be productive of f evening mists,' the results of which 

 are autumnal and intermittent fevers." And is not the ter- 

 restrial radiation of caloric, I would here ask, the cause of those 

 evening mists which favour the attacks of these disorders ? In- 

 deed it is remarkable to find that every locality pointed out 

 by the Doctor as productive of malaria, will be found to possess 

 one or other of those circumstances which promote the dissi- 

 pation of heat from the ground. It has long been known that 

 water and a grassy surface are excellent radiators of caloric ; 

 and the effects of this process — fogs, damps and dew — were ob- 

 served long before the cause of them was properly understood. 

 " A valley," says Mr. Daniell*, "is more liable to the effects 

 of radiation, than the tops or sides of hills ; and it is a well- 

 known fact that dew and hoar-frost are always more abundant 

 in the former than in the latter situations. The influence of high 

 hills is, however, often prejudicial to the valleys at their feet ; tor 

 the condensed and moist air rolls down their sides, and lodges 

 at the bottom: these, therefore, are protected from the chill, while 

 a double portion falls upon what many are apt to consider the 

 more sheltered situation. It is a very old remark, that the in- 

 jurious effects of cold occur chiefly in hollow places, and that 



* Meteorological Essays and Observations. 



frosts 



