294 WRITINGS OF JOSEPH HENRY. [1850 



the American Philosophical Society. All the complex phe- 

 nomena he had observed could be referred to a series of 

 oscillations in the discharge of the jar. If we adopt the 

 hypothesis of a single fluid, then we shall be obliged to ad- 

 mit that the equilibrium of the fluid after a discharge takes 

 place by a series of oscillations, gradually diminishing in 

 intensity and magnitude. He had been enabled to show 

 effects from five of these waves in succession. The means 

 used for determining the existence of these waves was that 

 of the magnetization of steel needles, introduced into the 

 axis of a'spiral. A needle of this kind it is well known is 

 susceptible of receiving a definite amount of magnetism, 

 which is called its saturation. Now if the needle be of such 

 a size as to be magnetized to saturation by the principal 

 discharge, it will come out of the spiral magnetized to a less 

 degree than that of saturation, by the amount of the adverse 

 influence of the oscillations in the opposite direction to that 

 of the principal discharge. If the quantity of electricity be 

 increased, the power of the second wave may be so exalted 

 that the needle will exhibit no magnetism ; the whole eff'ect 

 of the first or principal wave will be neutralized by the ac- 

 tion of the second. If the quantity of electricity be greater 

 than this, then the needle will be magnetized in an opposite 

 direction. If the electricity be still more increased, the 

 needle will again exhibit a change in its polaritj'', and so on 

 in succession, as the power of the successive waves is in- 

 creased. 



These experiments had been made several years ago, but 

 he had not given them in detail to the public, because he 

 had wished to render them more perfect. For the last three 

 and a half years all his time and all his thought had been 

 given to the details of the business of the Smithsonian Insti- 

 tution. He had been obliged to withdraw himself entirely 

 from scientific research ; but he hoped — now the Institution 

 had got under way, and the Regents had allowed him some 

 able assistants, — that he would be enabled, in part at least, 

 to return to his first love — the investigation of the phe- 

 nomena of nature. 



