270 MEMORIAL OF JOSEPH HENRY. 



differing deflections of the galvanometer needle "that the spot 

 emitted less heat than the surrounding parts of the luminous disk."* 

 A brief account of the results obtained by these researches given in 

 a letter to his friend Sir David Brewster, was read by the latter 

 at the Cambridge Meeting of the British Association in June, 1845.f 

 The determinations arrived at have been fully confirmed by the 

 later observations of Secchi and others. J 



In 1845, he contributed a paper to the Princeton Review, on 

 " Color Blindness ;" which although in the modest form of a literary 

 review of two Memoirs then recently published, (that of Sir David 

 Brewster in the Philosophical Magazine ; and that of Professor Elie 

 Wartman, of Lausanne, in the Scientific Memoirs,) supplied 

 original observations on this interesting department of the physi- 

 ology of vision. 



Miscellaneous Contributions. Henry's miscellaneous contribu- 

 tions to physical science are so numerous and varied, that only a 

 brief allusion to some of them can be afforded. In 1829, he 

 published quite an elaborate " Topographical sketch of the State of 

 New York, designed chiefly to show the general elevations and 

 depressions of its surface." And in later years he devoted much 

 attention to physical geography. He also made some geological 

 explorations and observations in the State of New York. He per- 

 formed at various times a good deal of chemical work (chiefly of 

 an analytical character), first as Dr. T. Romeyn Beck's assistant, || 



* Proceed. Am. Phil. Soc. June 20, 1845, vol. iv. pp. 173-176. 



t Report Brit. Assoc. 1845, part ii. p. 6. 



JP. ANGELO SECCHI during the years 1848 and 1849, (then a young man of thirty,) 

 was Professor of Mathematics at the College of Georgetown, D. C. and in the pre- 

 paration of his " Researches on Electrical Rheometry," published in the third 

 volume of the Smithsonian Contributions, (art. ii. 60 pp.) he received from Henry the 

 friendly assistance of apparatus and suggestions. It is interesting to refer to 

 Henry's introduction of Professor Secchi's first researches to the attention of the 

 Regents of the Smithsonian Institution, when the name was as yet wholly un- 

 known to the scientific world. "Another memoir is by Professor Secchi, a young 

 Italian of much ingenuity and learning, a member of Georgetown College. It 

 consists of a new mathematical investigation of the reciprocal action of two 

 galvanic currents on each other, and of the action of a current on the pole of a 

 magnet." (Smithsonian Report for 1849, p. 172, S. ed. and p. 164, H. R. ed.) Professor 

 Secchi was appointed Director of the Observatory at Rome, in 1850. 



g Trans. Albany Institute, vol. i. pp. 87-112. 



J " HENRY was then Dr. BECK'S chemical assistant, and already an admirable 

 experimentalist." Address before the Albany Institute, by Dr. O. Meads, May 25, 

 1871. (Trans. Albany Institute, vol. vii. p. 21.) 



