1853] WRITINGS OF JOSEPH HENRY. 315 



of mechanical power. Beneath the soil of our own great 

 coal basins there reposes power equivalent to the united 

 force of myriads of giants, ready (like Aladdin's Genius) to 

 be called into activity by the lamp of science, and as its 

 obedient slave to build cities, to transport palaces, or to re- 

 move mountains. There is no other locomotive power over 

 which man has any prospect of control in the least degree 

 comparable with this. 



I have made these remarks with reference to power, be- 

 cause mistakes on this subject are so frequent and so fatal. 

 Allow me, in the next place, to call your attention to some 

 other points having a direct bearing upon the progress of the 

 mechanic arts. 



In order that an important invention may be successful, 

 two conditions must be favorable: First: It must be possi- 

 ble; that is, the scientific principle on which it is to be 

 founded must be known. Second: The invention must be 

 wanted ; or in other words, it must be called for by the char- 

 acter and intelligence of the times, or rendered especially 

 desirable in a particular place by some peculiarity of climate, 

 topography, &c. 



With reference to the first position, it may be said that in 

 accordance with the well-known laws of permutation, an 

 almost infinite number of new combinations or inventions 

 may be formed from the present stock of scientific knowledge. 

 This is true : but the inventions thus produced must be re- 

 stricted as to kind, and though they be unlimited in num- 

 ber they are not so as to character. No combination ot 

 known principles, before the discovery of galvanism, was 

 sufficient for the invention, by the most ingenious synthetical 

 mind, of the electro-magnetic telegraph; but after the dis- 

 coveries made by Galvani and Oersted, this invention be- 

 came possible. 



In the history of the progress and development of a branch 

 of science a condition is reached when its principles become 

 applicable to some practical purpose, and it is instructive to 

 observe how at this period it suddenly as^mes in the public 

 mind a high degree of importance. The man who makes 



