624 ADDRESS OF PROFESSOR LOVERING. 
hole in the window shutter was enough to reveal the presence of 
the two boldest dark lines in the solar spectrum. Wollaston 
stood on the threshold of a rich development in science, but 
neither he nor his compeers were ready for it, and what he saw, 
novel as it was, attracted little attention. Spectrum analysis, in 
relation to light itself, began when Frauenhofer published, in 
1817, in the memoirs of the Bavarian Academy, an account of his 
experiments on the direct and reflected rays of the sun, on star- 
light, and various artificial sources of light: dispersing the rays 
by prisms of fine Munich glass and then receiving them into 4 
theodolite. Frauenhofer repeated some of his experiments in the 
presence of the younger Herschel, but for many years he had the 
field wholly to himself. A paper by Herschel on the colors of 
artificial flames acquires a new interest from what has been done 
more recently. Between 1830 and 1860, numerous physicists, 
ong whom are the well known names of Brewster, Miller, 
Wheatstone, Powell, Stokes, Gladstone, Becquerel, Masson, 
Van der Willigen, Pliicker, and Angstrém, were at work upon the 
facts connected with the emission of light by incandescent bodies 
and its absorption by gases and vapors. As early as 1830, Simms 
had placed a lens in front of the prism, with the slit in, the focus, 
and another lens behind the prism to form an image of the slit. 
The first hint of that pregnant fact, the reversal of the bright 
spectrum bands of flames, came from Foucault in 1849. His ex- 
periment was repeated at Paris, in 1850, in the presence of Sir 
William Thomson. It was reserved for a young physicist of 
Heidelberg, who was not born until seven years after Frauenhofer. 
laid the foundations, to place the keystune upon the structure on 
which many hands had labored: by demonstrating, in 1860, the 
law which is the theoretical basis of the chemistry of the heavens 
Kirchhoff, with admirable frankness, is careful to say that this law 
had been anticipated by others, especially by Angstrom and 
Balfour Stewart, although it had not been sharply stated oF 
severely proved. It is a singular fact that the mechanical ex- 
planation of the law, as it has been expounded by Kirchhoff, 
Angström, and Stokes, was partially enunciated one hundred years 
ago by the mathematician, Euler, when he said that every sub- 
stance absorbs light of the special wave-length which correspo 
to the vibration of its smallest particles. The 11th of July, 186» 
will be ever memorable in the history of science as being the day 
