-1859] WRITINGS OF JOSEPH HENRY. 311 



which although presented in the language of hypothesis, 

 yet really furnish the exact expression of a large class of facts. 



Hypotheses — well conceived and properly conditioned 

 by strict analogy, not only enable us, as above stated, 

 to embrace at one view a wider range of phenomena, but 

 also assist us in passing from the known to the unknown. 

 When rightly used they are the great instruments of dis- 

 covery, giving definite direction as to the experiments or 

 observations desirable in a particular investigation, and thus 

 marking out the line of research to be pursued in our en- 

 deavors to enlarge the bounds of the science of our day. We 

 think that the tendency of some minds, instead of being too 

 speculative is too positive; and while on the one hand there 

 is too much of loose, indefinite, and consequently of useless 

 speculation intruded upon science, on the other hand an evil of 

 an opposite kind is frequently produced by attempting to ex- 

 press scientific generalizations of a complex character with- 

 out the aid of proper hypotheses; and to this cause we would 

 principally ascribe the looseness of conception which fre- 

 quently exists in well-educated minds as to the connection 

 and character of physical phenomena. 



In accordance with the foregoing remarks we shall make 

 use of a theory to express the well-established principles of 

 electrical action, and from this endeavor to deduce such con- 

 clusions as are in strict conformity with the observed phe- 

 nomena. The intelligent reader who attentively studies this 

 theory, and exercises his reasoning faculties in drawing con- 

 clusions from it, will be able not only to explain many re- 

 markable appearances which would otherwise be entirely 

 isolated, but also to anticipate results, and to adopt means 

 to prevent unpleasant occurrences or to ward off dangers. 



The theory which we shall adopt is that invented by 

 Franklin, and extended and improved by Epinus and Caven- 

 dish. It is sometimes called the theory of one fluid, in con- 

 tradistinction to the theory of Dufay, of two fluids. The 

 two theories however do not differ so much as at first sight 

 might be supposed, and when expressed mathematically are. 

 essentially the same. 



