146 ON THE WORKS AND CHARACTER 



subject, shows his perfect understanding of the inductive 

 method, and the inherent indeterminateness of his analysis : 



" It is evident there must be a precise quantity in which the elements of 

 compounds are united together in them, otherwise a matter, which was not 

 a simple one, would be liable in its several masses, to vary from itself, accor- 

 ding as one or the other of its ingredients chanced to predominate; but 

 chemical experiments are unavoidably attended with too many sources of 

 fallacy for this precise quantity to be discovered by them ; it is therefore to 

 theory that we must owe the knowledge of it. For this purpose an hypoth- 

 esis must be made, and its justness tried by a strict comparison with facts. 

 If they are found at variance, the assumed hypothesis must be relinquished 

 with candor as erroneous ; but should it, on the contrary, prove, on a mul- 

 titude of trials, invariably to accord with the results of observation, as 

 nearly as our means of determination authorize us to expect, we are war- 

 ranted in believing that the principle of nature is obtained, as we then have 

 all the proofs of its being so, which men can have of the justness of their 

 theories : a constant and perfect agreement with the phenomena, as far as 

 can be discovered." 



The following passage, page 29, shows how clearly the 

 object to be attained was set forth in his own mind : 



" If the theory here advanced has any foundation in truth the discovery 

 will introduce a degree of rigorous accuracy and certainty into chemistry, 

 of which this science was thought to be ever incapable, by enabling the 

 chemist, like the geometrician, to rectify by calculation the unavoidable 

 errors of his manual operations, and by authorizing him to eliminate from 

 the essential elements of a compound those products of its analysis whose 

 quantity cannot be reduced to any admissible proportion. 



" A certain knowledge of the exact proportions of the constituent prin- 

 ciples of bodies, may likewise open to our view harmonious analogies be- 

 tween the constitutions of related objects, general laws, &c., which at 

 present totally escape us. In short, if it is founded in truth, its enabling 

 the application of mathematics to chemistry cannot but be productive of 

 material results." 



At the time his paper on the " Compounds of Fluorine" 

 was published, the composition of fluor spar was still a mat- 

 ter of doubt. The following is a sketch of a proposed 

 method for determining it: 



" If fluor spar, for instance, is a combination of oxide of calcium and 

 fluoric acid, and this is expelled from the oxide merely by the force of fire, 

 the decomposition of it will take place in closed vessels without the pres- 

 ence of oxygen or of water ; fluoric acid will be obtained ; and the weight 

 of this acid and the lime will be equal together to that of the original spar. 



" If the spar is metallic calcium and fluorine, and when heated in oxygen 

 absorbs this, and parts with fluorine, it is fluorine which will be collected 

 in the vessels, and its weight and that of the lime will together exceed that 

 of the spar by the oxygen of the lime." 



Further on he suggests the employment of vessels of 

 fluor spar for the examination of fluorine. He then dis- 

 cusses the phenomenon of intumescence as observed in 

 fluor spar and similar substances, in order to correct an 

 erroneous explanation of its nature that it was a "new state 



