OF ARTS AND SCIENCES. 481 



Professor Rowland's improvements in the diffraction-spectrum are 

 manifold, 1. He has substituted for the fiat plate on wliich 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 100,000, have covered only one inch. 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 arrange- 

 ments, 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. 6. The 

 spectrum obtained is the normal spectrum. In the words of a com- 

 petent authority on the subject, " the gratings of Mr. Rowland make 

 a new departure in spectrum-analysis." 7, Finally, his mathematical 

 exposition of the theoi-y of gratings has explained observed anomalies, 

 indicated the conditions of success, and prophesied the limits at which 

 future improvements in spectrum-analysis must stoj). 



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 medals which constitute the Rumford premium. 

 Count Rumford, in conveying this trust to the Academy through 

 President John Adams, expressed a preference 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 numerous and 

 valuable, and are sure of popular recognition and reward; but they 

 often come from the most unexpected quarters. No one can predict 

 what wonderful points of contact may be suddenly revealed between 

 a purely theoretical investigation and the practical utilities of life. 

 Meanwhile, a deeper insight into the laws of the material universe, 

 extorted from a reluctant Nature only after long and patient labor 

 and thought, and many disappointments, becomes a permanent posses- 

 sion for mankind ; and, as long as man does not live by bread alone, 

 it is for him a perennial blessing. The Academy, in awarding the 

 Rumford premium to you, has indicated the kind of scientific work 

 which, in its opinion, tends most to promote the highest good of 

 mankind. 



I ask you to accept, with these medals, my warm congratulations, 

 and the cordial good wishes of. all the members of the Academy here 

 assembled to administer Count Rumford's trust. 



VOL. XIX. (n. S. XI.) 31 



