276 Mr. Addison's Remarks on the bifluence of Terrestrial 



which, / believe, develops its existence in the air : whereas, if 

 these are cut down and the ground cleared, a good radiating 

 surface becomes immediately exposed, and the dissipation of 

 caloric with its accompanying effects directly ensues. — " A 

 portion of grass-plat," says Mr. Daniell in his Meteorological 

 Essays, " under the protection of a tree or hedge will generally 

 be found on a clear night to be eight or ten degrees warmer 

 than surrounding unsheltered parts ; and it is well known to 

 gardeners that less dew and frost are to be found in such si- 

 tuations than in those which are freely exposed." — Dr. Mac- 

 culloch in noticing the comparative healthiness of ancient and 

 modern Rome, thought it not unimportant to notice what 

 Theophrastus has stated with regard to the plain of Latium, 

 which this historian says was covered with laurel and myrtle- 

 trees of such a size as to be used in ship-building ; and this 

 remark, if terrestrial radiation has any thing to do with the de- 

 velopment of malaria, is not so fanciful as one of his reviewers 

 seems to imagine it*. Again, If terrestrial radiation is the cause 

 of the deleterious influence of those effluvia existing in the at- 

 mosphere, we are no longer surprised at finding rice-grounds, 

 which are kept in a constant state of wet or moisture during 

 the growth of the plants, prolific in the diseases which ma- 

 laria occasions. 



" Dr. Macculloch is convinced that the minute marshy 

 or swampy spots which occur in thousands of low situations, 

 whether on commons, near woods by road sides, or in innu- 

 merable other places where they hardly ever attract notice, — 

 are productive of malaria ; though their limited range of action 

 generally renders their power insensible, unless when houses 

 happen to be erected in their vicinity." — " In how far meadows 

 which cannot be called marshy are capable of producing ma- 

 laria, is an intricate and entangled question. It appears cer- 

 tain, however, that there are many tracts of meadow or of al- 

 luvial land not marshy, and often not intersected by ditches, 

 at least in a conspicuous manner, which are the sources of 

 malaria all over Europe." Essay, p. 69. — " Such is the case 

 with all the alluvial tracts at the entrances and sometimes at 

 the exits of the lakes of Switzerland and elsewhere ; and in 

 places innumerable where there is no proper marsh, nor even 

 an approach to such a character, but where the prevalent dis- 

 eases must be owing to malaria." — " Volney, while travelling 

 in America, has averred that every valley in the country which 

 he visited produced the fevers of malaria, enumerating among 

 the sources of this poison not only marshes and wood, but 



* Medico-Chirurgical Review, January 1828. 



rivers, 



