OF ARTS AND SCIENCES. 483 



camera should move along the arc of a circle at one end of a diameter, 

 upon the other end of which the grating was placed, and always remain 

 in focus. With this apparatus, onB can do in an hour what formerly 

 took days. Moreover, the spectra obtained are always normal spectra, 

 and every inch on a photograph represents a certain number of wave- 

 lengths. 



After finishing my apparatus, I found it necessary to study photog- 

 raphy ; and I "therefore devoted much time to this subject, and made 

 a special study of all known emulsions. I discovered that an emulsion 

 containing eocene ienabled me to photograph from the violet down to 

 the D line ; and other emulsions were used for the red rays. I have 

 also been engaged in enlarging my negatives, and in printing from 

 these negatives. On these enlarged photographs, lines are doubled 

 which have always been supposed to be single. The E line is easily 

 doubled. My map of wave-lengths is based upon Professor Charles 

 S. Peirce's measurements of the wave-length of a line in the green 

 portion of the spectrum. 



The following paper was presented by title : — 

 " Deducing from one Epoch to another Stars very near the 

 Pole." By William A. Rogers. 



Seven hundred and seTsntieth Meeting. 



March 12, 1884. — Stated Meeting. 



The President in the chair. 



The President announced the death of Johann F. J. 

 Schmidt, of Athens, Foreign Honorary Member ; and of 

 George Engelmann, of St. Louis, Associate Fellow. 



The Corresponding Secretary read an invitation from the 

 Royal Society of Canada to attend its third annual meeting, 

 at Ottawa. 



Professor Pickering spoke of the importance of a represen- 

 tation before the legislature in I'egard to a new topographical 

 map of the State. The chair appointed the following com- 

 mittee to consider this subject : — 



Messrs. Edward C. Pickering, Asa Gray, and Samuel H. 

 Scudder. 



