258 MEMORIAL OF JOSEPH HENRY. 



Meteorology. — From an early date Henry took a deep interest 

 in the study of meteorology: not only on account of its practical 

 importance, but from its relation to cosmical physics, and because 

 from the very complexity and irregularity of its conditions, it 

 challenged further investigation and stood in need of larger gener- 

 alizations. His early association with Dr. T. Romeyn Beck in 

 the first development of the system of meteorological observations 

 established in the State of New York, has already been referred to 

 in the sketch of his " Early Career." (Page 212.) This active and 

 zealous co-operation continued from 1827 to 1832; or as long as he 

 resided in Albany. 



In September of 1830, he commenced a series of observations 

 for Professor Renwick of Columbia College, to determine the 

 magnetic intensity at Albany. With the assistance of his brother- 

 in-law, Professor Stephen Alexander, these observations were con- 

 tinued daily for two months.* In April, 1831, a second series of 

 observations was commenced; in the course of which his attention 

 was attracted by a great disturbance of the needle during the 

 time of a conspicuous "aurora" on the 19th of April, 1831. At 

 noon of the 1 9th the oscillations were found to be perfectly accord- 

 ant with previous ones, but at 6 o'clock p. m. a remarkable increase 

 of magnetic intensity was indicated. At 10 o'clock of the same 

 evening, during the most active manifestation of the aurora, the 

 oscillations of the needle were again examined. " Instead of still 

 indicating as at 6 o'clock an uncommonly high degree of magnetic 

 intensity, it now showed an intensity considerably lower than usual." 

 Thus, designating the normal intensity at the place as unity, at 6 

 o'clock it had increased to 1.024, and at 10 o'clock had subsided to 

 0.993, which according to Hansteen's observations is the usual 



* The needles employed in these observations were a couple received by Professor 

 Renwick from ('apt. 8ahine, — one of which had belonged to Professor IIansteen 

 of Norway. "They were suspended according to the method of Ilanstcen in a small 

 mahogany box, V)y a single fiber of raw silk. The box was furnished with a glass 

 cover, and had a graduated arc of ivory on the bottoni to mark the amplitude of the 

 vibrations. In using this apparatus, the timeof three hundred vibrations was noted 

 by a quarter-second watch, well regulated to mean time; a register being made at 

 the end of every tenth vibration, and a mean deduced froni the whole, taken as the 

 true time of the three hundred vibrations. Kxjieriments carefully made with this 

 apparatus M'ere found susceptible of considerable accuracy;"' the individual observa- 

 tions not differing front the mean number, ordinarily more than one-thousandth. 

 (Silliman's Am. Jour. Sci. April, 1832, vol. xxii. p. Ho.) 



