330 PHILOSOPHICAL TRANSACTIONS. [aNNO 1778. 



clay soils appear to be favourable to health ; they emit no kind of septic or 

 noxious effluvia. 



Exp. 28. Wet sand was tried in the same manner, and found to have no 

 noxious effect on air: from which it may be concluded, that the general notion 

 of the salubrity of sandy soils is founded on truth. 



We may now conclude with recapitulating a few inferences, which seem to be 

 proved by the preceding experiments. 1 . The atmospheric air is rendered worse 

 by a long continuance of dry weather. 2. It is purified by rains and winds, 

 especially westerly ones. 3. It is considerably worse in cities and large towns, 

 than in the country, even at a small distance. 6. It is quickly poisoned by the 

 effluvia from animal bodies, even while perfectly sweet and free from putridity. 

 7. Vegetable matters, when not in a growing state, have a similar effect, and in 

 a degree equally powerful. 8. And this is not any ways owing to their aroma 

 or odorous parts, p. Phlogiston rises alone. lO. Phlogiston is imperceptible 

 to the smell, perse, ll. Phlogiston is, per se, pestilential. 12. The absence 

 of disagreeable smells is by no means a criterion of the healthful state of jails, 

 hospitals, &c. or of their freedom from infection. 13. Mere odour does not 

 injure the air, nor do volatile alkalies. 14. The air is generally pure over waters. 

 15. The air is greatly injured by the effluvia from the thick mud of bogs and 

 marshes. l6. But this is much obviated by laying them under water. 17. Air 

 is not hurt by such mud when perfectly dry. 18. Air is also infected by the dirt 

 of the streets. IQ. Pure loamy vegetable earth has little of such effect. 20. 

 Air is not at all polluted by pure clay soils. 21. Nor by those of pure sand. 



XIV^. An Account of the Earthquake felt at Manchester and other Places, Sept, 

 14, 1777. By Mr. Thomas Henry, F. R. S. p. 221. 

 On the morning of the day on which the earthquake happened, Mr. H. was 

 confined to his bed beyond the usual hour by a head-ache, with which he was 

 generally troubled previous to any storms or considerable changes in the atmos- 

 phere. About 5 minutes before 1 1 o'clock, he was alarmed by a noise which 

 seemed as if it might have proceeded from a large bale of goods thrown down on 

 a boarded floor below stairs : the house shook. He called out to his wife, who 

 was in an adjoining closet, to know what could have fallen ; when instantly he 

 was astonished by such a rattling noise at the north east corner of the house, 

 that he cried out that a part of the house (which had been built but a few years, 

 and was not so firmly connected with the old part as it should have been) was 

 fallen ; and in this opinion he was immediately confirmed by a 3tl and more 

 violent crash, resembling the tumbling down of a large and lofty wall. Each of 

 these noises was succeeded by a separate concussion. These events must have 

 taken up the space of at least half a minute. During that time he got out of 



