(h t^e Fetid Gas of Drain f. 435 



iron, particularly when their particles are duly arranged, for then they are expofed to the 

 power of the great general magnet, which a£ls on them in proportion to this arrangement 

 and their affinity to iron. 



0/ Inclination and Declination. 



Thefe phjenomena, which are fo different in different parts of the globe, a«id even in 

 different feafons and hours of the day, not being as yet noted with fufficient certainty and 

 precifion, I fhall for the prefent decline entering into their explanation. 



VIII. 



On the Fetid Gas of Drains. 



SIR, 



London, Afay 16, 1800. 



JL HERE is a phenomenon which occurs too frequently for the comfort and eafe of many 

 of the inhabitants of this and other towns which have fubterraneous drains, and has not 

 been explained as I can yet find by reading or enquiry. Previous to, or about the time of 

 the late change from fair to frequent and continued rains, the apertures of the 

 common fewers, or great public drains communicating with the ftreets as well as with 

 houfes, privies, &c. emitted a well-known and abominably difgufting fmcll, which is often 

 perceived upon change of weather. It is alfo obfervable in fome houfes that this fmell is 

 always more or lefs predominant when the windows are fliut in at night. Perhaps I may 

 be troubling you upon a very well-known fubjedl, when I requeft you will explain thefe 

 fads, and point out the remedy ; but I am fure, however, that many of your readers would, 

 be glad to have your thoughts upon it, as well aS 



Your obliged reader, 



S. S, 



The fubjed to which the enquiries of S. S. are direded is, in fad, but little underflood. 

 The emifTion of fetid gas from the drains is found to take place when the barometer falls ; 

 and perhaps alfo upon changes of the thermometer, though I am difpofed to think this laft 

 is not the cafe. The offenfive gas which thus rifes from its fubterraneous fituation con- 

 fifls, probably, for the moft part of fulphurated hydrogen, together with humid efHuvia and 

 putrefcent matter. Houfes which are fubjed to this infedion are remarkable for the fpeed 

 with which filver plate becomes blackened, even when the prefence of tlie gas is not per- 

 ceptible to the inhabitants ; and they are alfo charaderillically remarkable for difeafe and 



mortality. 



