VOL. XV.] PHILOSOPHICAL TRANSACTIONS. 155 



Neither is efficacy confined to organical bodies, but extends also to inor- 

 ganicalones; as is evident from the sympathy of strings; the ringing of a glass 

 to such a note; as likewise some echoes answering only certain sounds ; and 

 the like. The mistake likewise is as great when men look upon divers bodies 

 to have their parts in a state of absolute rest, when they are in a state of ten- 

 sion, or compression. Instances of this are the sudden cracking of glasses that 

 seem to be well nealed, the scaling of well heated copper, the brittleness of 

 mixtures of metals, all which and the like probably proceed from contraction. 

 The last main cause why such motions are overlooked, is our being used to the 

 sensible motions of solid bodies, where as many effects proceed from the in- 

 testine motions produced in and among the parts of the same body ; such as 

 tools being over-heated, and so losing their temper; the breaking of optic 

 glasses in grinding; bodies becoming electrical and odorous by rubbing, and the 

 like; from all which he concludes, that such local motions as are wont to be 

 past by unobserved, may have a notable operation on such bodies as are 

 peculiarly disposed to admit it, and so have a large share in natural produc- 

 tions. 



In the discourse on some unheeded causes of the salubrity and insalubrity of 

 the air, he confines himself to the impregnation it receives from subterraneous 

 effluvia. Of these he makes two sorts, some constantly are sent up into the 

 air, which he calls ordinary emissions ; others ascend only at times, these are 

 extraordinary emissions ; these again are periodical or fortuitous. This doctrine 

 he endeavours to illustrate by asserting, first, that in divers places the salubrity 

 or insalubrity of the air considered in the general, may in good part be due to 

 subterraneous expirations, especially to those he before called ordinary emissions, 

 for this he appeals to experience, which finds some places more healthy than 

 the manifest qualities would permit one to expect ; this effect he therefore 

 ascribes to the friendly effluvia from the earth, and argues from the observa- 

 tions in Hungary, and Bohemia, where the air is impregnated with mineral 

 exhalations, suitable to the ore the earth contains under it. He affirms it also 

 probable, that in divers places some endemical diseases do at least in part 

 depend upon subterraneous steams, especially where the cause of the distem- 

 per cannot otherwise be accounted for, if together with this we consider the 

 perviousness of human bodies, and the penetrating quality of mineral expira- 

 tions, of which he gives many experiments. 



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