Vlll PRINCIPLES OF CHEMISTRY 



sophical principles of our science form the chief theme of the work. 

 In former times sciences, like bridges, could only be built up by 

 supporting them on a few deep abutments and long girders. In 

 addition to the exposition of the principles of chemistry, it has 

 been my desire to show how science has now been built up like 

 a suspension bridge, supported by the united strength of a number 

 of slender, but firmly-fixed, threads, which individually are of 

 little strength, and has thus been carried over difficulties which 

 before appeared impassable. In comparing the science of the past, 

 the present, and the future, in placing the particulars of its re- 

 stricted experiments side by side with its aspirations for unbounded 

 and infinite truth, and in restraining myself from yielding to a bias 

 towards following the most attractive representation, I have en- 

 deavoured to incite in the reader a spirit of inquiry, which, unsatis- 

 fied with speculative reasonings alone, should subject every idea 

 to experiment, excite the habit of stubborn woi-k, necessitate a 

 knowledge of the past, and a search for fresh threads to complete 

 the bridge over the bottomless unknown. Experience proves that 

 it is possible by this means to avoid two equally pernicious extremes, 

 the Utopian a visionary contemplation which proceeds from a 

 current of thought only and the realistic stagnation which is 

 content with bare facts. In sciences like chemistry, which treat 

 of ideas as well as of the substances of nature, experience demon- 

 strates at every step that the work of the past has availed much, 

 and that without it it would be impossible to advance ' into the 

 ocean of the unknown/ We are compelled to value their history, 

 to cast aside classical illusions, and to engage in a work which not 

 only gives mental satisfaction but is also practically useful. 1 



1 Chemistry, like every other science, is at once a means and an end. It is a 

 means of attaining certain practicable aspirations. Thus, by its assistance, the 

 obtaining of matter in its various forms is facilitated ; it shows new possibilities 

 of availing ourselves of the forces of nature, indicates the methods of preparing 

 many substances, points out their properties, etc. In this sense chemistry is 

 closely connected with the work of the manufacturer and the artisan, its sphere 

 is active, and is a means of promoting general welfare. Besides this honourable 

 vocation, chemistry has another. With it, as with every other elaborated science, 

 there are many lofty aspirations, the contemplation of which serves to inspire its 

 workers and partisans. This contemplation comprises not only the principal data 



