568 PHILOSOPHICAL TRANSACTIONS. [aNNO 1779. 



If dephlogisticated air be shaken in the tube, in the manner above-mentioned, 

 not only it does not increase its bulk, but it begins to diminish from the very 

 beginning of the operation, and it continually loses more and more of its bulk, 

 and with its bulk of its purity. This last mentioned property of dephlogisticated 

 air seems to show, that this is a fluid very different from common air, because 

 it has its peculiar properties by which it differs from common air, not from more 

 to less only, but entirely; as is shown by the property tiiis fluid has of being 

 absorbed by water; whereas common air receives an increase of bulk and elasti- 

 city by being shaken in water. 



All that he had been saying above, in order to give an idea of his method, 

 and the words he uses to express the diminutions made by the mixture of nitrous 

 air and other kinds of respirable air, is not sufficient to obtain results constant 

 and certain, so as to deduce any consequences from them. Even after all the 

 elements are corrected, and all the causes of error hitherto unknown or neglected 

 by the most diligent observers, are avoided, it is absolutely necessary to follow 

 always a constant and equal method, not only in the act of introducing the va- 

 rious kinds of air into the tube, but also after the mixture of the 2 kinds of air. 

 He had not the least hesitation in asserting, that the experiments made to ascer- 

 tain the salubrity of the atmospherical air in various places, in different countries 

 and situations, mentioned by several authors, are not to be depended on ; be- 

 cause the method they used was far from being exact, the elements or ingre- 

 dients for the experiment were unknown and uncertain, and the results very dif- 

 ferent from each other. 



When all the errors are corrected, it will be found, that the difference between 

 the air of one country and that of another, at different times, is much less than 

 what is commonly believed, and that the great differences found by various ob- 

 servers are owing to the fallacious effects of uncertain methods. This he advances 

 from experience; for when he was in the same error, he found very great differ- 

 ences between the results of the experiments of this nature which ought to have 

 been similar; which diversities he attributed to himself rather than to the method 

 he then used. At Paris he examined the air of different places at the same time, 

 and especially of those situations where it was most probable to meet with in- 

 fected air, because those places abounded with putrid substances and impure ex- 

 halations; but the differences he observed were very small, and much less than 

 what could have been suspected, for they hardly amounted to -jL of the air in the 

 tube. Having taken the air of the hill called Mont Valerien, at the height of 

 about 500 feet above the level of Paris, and compared it with the air of Paris 

 taken at the same time, and treated alike, he found the former to be hardly ^ 

 better than the latter. In London he had observed nearly the same. The air of 

 Islington and (hat of London suffered an equal diminution by the mixture of ni- 



