42 



ascribed in this account to Cavendish, ivith its date of May 1783, is, from 

 the beginning to the end, as to its existence, and all its details, a fiction : 

 it is easy to conceive a confusion of recollection which might lead a 

 lecturer to substitute his own ideas of what an experiment might 

 have been for what it was, or to confound the experiments of dif- 

 ferent persons on the same subject, though this is scarcely excusable 

 where the statement is one professing to adjust their respective claims. 

 Let us suppose then such a confusion to have led to the ascrip- 

 tion to Cavendish of the experiments of the French chemists ; but how 

 shall we account for the particularity of the fictitious date of May 1783 

 for the time of Cavendish's discovery ? Cavendish had not said a word 

 about May ; he had said that the experiments which constituted his 

 claim to that discovery were made in the summer of 1781 ; he had not 



tried the effect of almost every substance on it : he also tried the effect of the 

 electrical shock and spark. As he expected, he found that it was expanded 

 by it, but could not be inflamed by it in close vessels, unless mixed with com- 

 mon air. In this state it fired with a violent explosion. He was particularly 

 surprised at the great diminution of bulk, — finding that a mixture of one part 

 of inflammable air, and two of common air, might be made to contract into 

 half the bulk, and that it was now phlogisticated air. Having already dis- 

 covered the vital air, he fired a mixture of these, and found that when two 

 parts of inflammable air and one of vital air were exploded together, it collapsed 

 into almost nothing, or nearly the whole disappeared. Mr. Warltire, who as- 

 sisted in these experiments, observed that the inside of the vessel in which 

 the deflagration had been made, was always moistened with dew. Dr. 

 Priestley naturally ascribed this to moisture, which probably adhered to the airs 

 employed, as they were always produced in processes in which water in some 

 form or other was present. These experiments loere made about the year 1782. 

 [1781 is the true date both of the experiments really made by Priestley and 

 Warltire, which include no such fact as that alleged above, and those of 

 Cavendish here confounded with them.] 



" My friend Mr. Watt had taken great interest in these experiments of Dr. 

 Priestley's, and communicated his opinion concerning them to M. de Luc, in 

 a letter dated April 1783. [The true date of the experiments, here confused with 

 those of 1781, is April 1783, that of the letter is Nov. 1783.] This letter is, 

 in part, a transcript of one written some months before to Dr. Priestley, with 

 a desire that it should be communicated to the Royal Society. [The true date 

 is April 1783.] In this he declares his opinion, that the water observed in 

 these experiments arose from the combination of two airs ; and savs that 

 water is the compound of dephlogisticated or vital air, and inflammable air, 

 deprived of their latent heats ; and that dephlogisticated air is water deprived 

 of its phlogiston (i. e. of the inflammable air), in an aerial form, that is, satu- 

 rated with the matter of light and heat. Dr. Priestley did not communicate 

 this to the Society, because (he says) some exjjeriments which he had made since 



