- 
FEBRUARY 29, 1884. | 
only so far as a comparison of the size and mass of a 
body gives a measure of its density. That an instru- 
ment would be invented or developed which would 
complement the mechanics of the heavens by the 
chemistry of planets, comets, and stars, so that a 
physical observatory would become a necessary ad- 
junct of the old observatory, was beyond the hope of 
the most sanguine astronomer, down to the moment 
of its actual realization. 
Newton owes his singular fame, not exclusively to 
his discovery and expansion of the law of gravitation, 
but partly to his experimental researches in. optics. 
That he did not recognize the dark lines in the solar 
spectrum has been explained by the statement that 
he was obliged to use the eye of an assistant in these 
experiments, on account of aninjury tohisown. Be 
this as it may, the existence of these lines was first 
known to Wollaston in 1802; and from that moment 
= VEESRLGAN AGA 
ASR OWAGAN == 
the spectroscope and spectrum-analysis, as we now 
understand them, were possibilities. 
Although Fraunhofer made a careful study of 
these lines in 1824, and Brewster, Herschel, Talbot, 
Draper, and many others pursued the inquiry by way 
of experiment and explanation, and stood upon the 
threshold of a great discovery, the spectroscope and 
spectrum-analysis, as practical realities, date from 
the investigations of Kirchhoff and Bunsen in 1862. 
Not only does the spectroscope carry chemistry into 
regions tenanted only by planets, comets, stars, and 
nebulae, and reveal motions in the direction of the 
line of vision, otherwise hopelessly beyond recogni- 
tion, but it competes with the ordinary chemical 
analysis of bodies which can be handled, and has 
detected new substances which had escaped the 
vigilance of the chemist. Some of these results can 
be realized with simple instruments: others require 
a compound spectroscope consisting of a battery 
of prisms. It was a great step in the way of sim- 
plicity and ease of manipulation, when the diffraction- 
SCIENCE. 
257 
spectrum, produced by fine lines ruled upon glass or 
metal, was substituted for the spectrum produced by 
the combined refractions of many prisms. And here 
we touch upon the researches of Professor Rowland 
in light, which enhance his claim to the Rumford 
premium. 
Professor Rowland’s improvements in the diffrac- 
tion-spectrum are manifold. 1. He has substituted 
for the flat plate on which the grating was formerly 
ruled a spherical or cylindrical surface. 2. He has 
ruled these lines to such a degree of fineness that 
5,000, or 42,000, or even 160,000, have covered only 
oneinch. 3. This exquisite work was executed by a 
machine of his own invention, and produced spectra 
free from the so-called ghosts which result from 
periodical inequalities in the ruling. 4. By making 
the curvature of the ruled plate discharge the office 
of a lens, he has avoided absorption at the violet end 
of the spectrum. 5. By his simple mechanical ar- 
rangements, different parts of the spectrum can be 
photographed with a great economy of time, and 
with such excellence of definition that old lines are 
subdivided, and new ones spring into visibility: in 
the words of a competent authority on the subject, 
‘the gratings of Mr. Rowland make a new departure 
in spectrum-analysis.’ 6. Finally, his mathematical 
exposition of the theory of gratings has explained 
observed anomalies, indicated the conditions of suc- 
cess, and prophesied the limits at which future im- 
provements in spectrum-analysis must stop. 
PROFESSOR ROWLAND, It is now my duty, and 
certainly it is a most agreeable one, to present to you, 
in the name of the academy, the gold and silver med- 
als which constitute the Rumford premium. Count 
Rumford, in conveying this trust to the academy 
through President John Adams, expressed a prefer- 
ence for such discoveries as should, in the opinion 
of the academy, tend most to promote the good of 
mankind. The practical applications of science are 
