DISCOURSE OP W. B. TAYLOR. 269 



with three slits each, he was able to make simultaneous star-like 

 "photographs" on the substance, of the two extreme portions of the 

 spark and of a middle point: and while the latter point "exhibited 

 a feeble phosphorescence for two or three seconds " only, the two 

 former " continued to glow for more than a minute :" and yet the 

 middle of the spark appeared to the eye quite as vivid as its ex- 

 tremities. It was also observed that while a sensitive daguerreo- 

 type plate received no impression from the electric spark, inversely 

 another similar plate exposed for several minutes to the direct light 

 of the full moon received a photographic impression, while the 

 lime similarly exposed, exhibited no phosphorescence.* 



As a striking illustration of the closely allied phenomenon of 

 fluorescence, Henry was afterward accustomed on the occurrence 

 of a bright aurora, to expose a sheet of paper written or figured 

 with a solution of bisulphate of quinia to the auroral light, when 

 the characters (quite invisible by lamp-light or even by day-light) 

 would distinctly glow with a pale blue light; indicating the 

 electrical nature of the meteor. 



In January, 1845, in conjunction with Professor Stephen Alex- 

 ander, he instituted a series of experimental observations on the 

 relative heat-radiating power of the solar spots. On the 4th of 

 January a large spot through which our terrestrial globe could have 

 been freely dropped, (having been estimated at more than 10,000 

 miles in diameter,) favorably situated near the middle of the disk, 

 was examined with a telescope of four inches aperture. A screen 

 having been arranged in a dark room, with a thermo-electric 

 apparatus behind it and having its terminal or pile just projecting 

 through a hole in the screen, the image of the spot was received upon 

 it, giving a clearly denned outline about two inches long and one 

 inch and a half wide. By a slight motion of the telescope the spot 

 could readily be thrown on or off the end of the pile as desired. A 

 considerable number of observations indicated very clearly by the 



* Proceed. Am. Phil. Soc. May 26, 1843, vol. iii. pp. 38-44. This interesting but ob- 

 scure subject although apparently connected with the phenomenon of "fluores- 

 cence" has yet an entirely distinct phase in its abnormal continuance of lumin- 

 osity, similar to the familiar effect of a thermal impression. It is possible how- 

 ever that the conversion of wave-periodicity (wave-length), shown by Stokes to be 

 the characteristic of fluorescence, may require time for its full development. 



