522 The Smithsonian Institution 



pregnant principle that the Institution should do nothing which 

 can be equally well done through other agencies. It is to the 

 adoption of this rule, the farsighted wisdom of which cannot 

 be questioned, that we must attribute an apparent lack of con- 

 tinuity in its operations in physical science, which is probably 

 equally noticeable elsewhere; for its policy has been to do 

 what could not be done otherwise ; to help only when help 

 was absolutely necessary. 



In taking account of the contributions to the various de- 

 partments of physics which the cooperation of the Smithso- 

 nian Institution has made possible, or with which it has been 

 conspicuously related or associated, one must necessarily 

 begin with the splendid discoveries of its first distinguished 

 head. It is true that many of the most important of these 

 were actually made during that eventful period of his life 

 which preceded his appointment as Secretary of the In- 

 stitution, but it is also true that many of them did not find 

 their full development until after that date, and, indeed, it is 

 only during the last decade that some of the most important 

 have received recognition at their proper value. 



Henry's contributions to physics covered a wide range, but 

 they are most numerous along the line of electricity, magnet- 

 ism, acoustics, and meteorology. They were originally pub- 

 lished, for the most part, in the earlier volumes of the 

 American Journal of Science, but much of his later work 

 was, until recently, to be found only by searching the pages 

 of various government publications, or in the transactions 

 of several of the learned societies. In 1886, however, by di- 

 rection of the Regents of the Institution, the then Secretary, 

 Professor Baird, published a collection of his " Scientific 

 Writings " in two large and handsome volumes, which are 

 among the most important of the Smithsonian contributions 

 to physics. As already stated, within a few years there has 



