24 P^'oceedings of the Royal Physical Society. 



pneumatic chemistry ; and no doubt his most valuable dis- 

 coveries, especially in this department, entitle him to all 

 praise, and yet he was not exactly the kind of man we would 

 select as being eminently fitted for scientific investigation. 

 He had an idea, I conceive, that discoveries are made by 

 chance, and although he made a great many most impor- 

 tant discoveries, he seems to have passed over without grasp- 

 ing, or, at all events, without rightly explaining, results which 

 he obtained, and which might, if they had been properly 

 utilised, have proved most valuable by paving the way for 

 obtaining others. Thus, for example, although he had noticed 

 the formation of water by the burning of a mixture of 

 hydrogen and oxygen, he seems to have passed it over — 

 wonderful as it must have appeared to him — without giving 

 any real explanation of the phenomenon. This discovery, 

 that is, the discovery of the composition of water, which 

 might have belonged to Priestley, is ascribed, and rightly so, 

 to Sir Henry Cavendish. Priestley not only produced the 

 water by causing the hydrogen and oxygen to combine, but 

 he observed and noted it, leaving the explanation of what he 

 had done to be given by others. Curious as it may seem, 

 Priestley was a firm believer in the phlogistic theory, and con- 

 tinued so till the last, although he, by his great life's work, had 

 done more than any one else to bring about its overthrow. 



Contemporary with Priestley, and like him in being the 

 author of some valuable discoveries, and yet very unlike 

 him in the mode of doing his work, was the celebrated Sir 

 Henry Cavendish. Cavendish was born in the year 1731, 

 and being of independent means, he devoted himself ex- 

 clusively to scientific pursuits. He worked zealously and 

 faithfully, and though he did not make so many brilliant 

 discoveries as Priestley, or perhaps do so much work, yet 

 what he did was done more thoroughly and completely. His 

 work was greatly quantitative, and as proof of the accurate 

 nature of his mode of carrying on his investigations, we find 

 him in his experiments with gases making corrections for 

 changes caused by the alterations of temperature and pressure, 

 a refinement somewhat unusually observed, I am inclined to 

 think, in these early days. The great work with which the 



