26 



aiUlitional weight fiotn the authorities hy which they are siipjiorted, till at last, 

 they are received, even liy men of genius, as fundamental truths. 



"The only method of preventing such errors from taking place, and of cor- 

 recting them when formed, is to restrain and simplify our reasoning as much as 

 possible. This dei)ends only on ourselves, and the neglect of it is the only source 

 of our mistakes. We must trust to nothing but facts; these are presented to us 

 by nature and can not deceive. We ought, in every instance, to submit our 

 reasoning to the test of experiment, and never to search for truth but by thfr 

 natural road of experiment and observation. Thus mathematicians obtain thfr 

 solution of a problem by the mere arrangement of data, and by reducing their 

 reasoning to such simple steps, to conclusions so very obvious, as never to lose- 

 sight of the evidence which guides them. 



"Thoroughly convinced of these truths, I have imposed upon myself as a. 

 law never to advance but from what is known to what is unknown; never to form 

 any conclusion which is not an immediate consequence necessarily Howing from 

 observation and experiment; and always to arrange the facts, and the conclusions, 

 drawn from them in such an order as shall render it most easy for beginners in 

 the study of chemistry thoroughly to understand them. Hence I have been 

 obliged to depart from the usual order of courses of lectures and of treatises on 

 chemistry, which always assumes the first principles of the science, as known, 

 when the pupil or the reader should never be supposed to know them till they 

 have been explained in subsequent lessons. In almost every instance these begin 

 by treating of the elements of matter, and by explaining the table of atiinities, 

 without considering that, in so doing, they must bring the principal phenomena 

 of chemistry into view at the very outset; they make use of terms which have 

 not been defined and suppose the science to be understood by the very persons 

 they are only beginning to teach. It ought likewise to be considered, that very 

 little of chemistry can be learned in a first course, which is hardly sufJicient to 

 make the language of the science familiar to the ears, or the apparatus familiar 

 to the eyes. It is almost impossible to become a chemist in less than three or four 

 years of constant application." 



These statements are no less true to-day than one hundred years ago. No 

 less apposite is the following, referring to the work to be done in chemistry : 



"This is a vast field for employing the zeal and abilities of young chemists, 

 ^hom I would advise to endeavor rather to do well than to do much. ■■ * * 



Every edifice which is intended to resist the ravages of time should be built on a 

 sure foundation; and, in the present state of chemistry, to attempt discoveries by 



