PREFACE. 



AFTER I had composed the following Essay, I naturally felt. 

 anxious to become acquainted with what had been effected by 

 former writers on the same subject, and, had it been practicable, 

 I should have been glad to have given, in this place, an his- 

 torical sketch of its progress; my limited sources of information, 

 however, will by no means permit me to do so ; but probably 

 I may here be allowed to make one or two observations on the 

 few works which have fallen in my way, more particularly as an 

 opportunity will thus offer itself, of noticing an excellent paper, 

 presented to the Royal Society by one of the most illustrious 

 members of that learned body, which appears to have attracted 

 little attention, but which, on examination, will be found not 

 unworthy the man who was able to lay the foundations of 

 pneumatic chymistry, and to discover that water, far from being 

 according to the opinions then received, an elementary sub- 

 stance, was a compound of two of the most important gases in 

 nature. 



It is almost needless to say the author just alluded to is the 

 celebrated CAVENDISH, who, having confined himself to such 

 simple methods, as may readily be understood by any one pos- 

 sessed of an elementary knowledge of geometry and fluxions, 

 has rendered his paper accessible to a great number of readers; 

 and although, from subsequent remarks, he appears dissatisfied 

 with an hypothesis which enabled him to draw some important 

 conclusions, it will readily be perceived, on an attentive perusal 

 of his paper, that a trifling alteration will suffice to render the 

 whole perfectly legitimate*. 



* In order to make this quite clear, let us select one of CAVENDISH'S proposi- 

 tions, the twentieth for instance, and examine with some attention the method 



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