168 PROCEEDINGS OF THE AMERICAN ACADEMY 



Jackson. Mr. Alger has also recognized some minute crystals of 

 topaz on the green felspar. It appears, therefore, that the granite 

 rocks of Rockport are far from being barren in minerals of scientific 

 value. 



A report from tlie Rumford Committee was presented, and, 

 there being no quorum for the transaction of business, was 

 referred to an adjourned meeting. 



Five hundred and twenty-fifth Meeting. 



September 8, 1863. — Adjourned Stated Meeting. 



The President in the chair. 



The President read a letter from Professor Hitchcock, accom- 

 panying a memoir entitled " Supplement to the Ichnology of 

 New England." Also a note from Professor Eliot, resigning 

 his place as a member of the Rumford Committee. 



Professor Lovering called up the recommendations of the 

 Rumford Committee, which were read at the previous meeting 

 and referred to this meeting for the action of the Academy. 

 On the motion of Dr. Beck, it was 



Voted, That the sum of three hundred dollars be paid from the in- 

 come of the Rumford fund to Mr. O. N. Rood, to be used by him in 

 making investigations on the subject of the physical relations of the 

 iodized plate to light ; — the results of these investigations to be com- 

 municated to the Rumford Committee, and to be offered by them for 

 publication in the Memoirs of the American Academy of Arts and 

 Sciences. 



Professor Bond gave an account of the construction of ach- 

 romatic object lenses by Dr. Steinheil of Munich, according 

 to the method of Gauss ; this being the first successful attempt 

 at working lenses in the form proposed by Gauss for the correc- 

 tion of chromatic aberration, independently of spherical aberra- 

 tion. Lenses thus constructed have the advantage of combin- 

 ing large apertures with short focal lengths, and thus require 

 only short telescope-tubes, which are least liable to errors from 

 flexure. The thickness of the glass needed for producing 

 lenses of the requisite curvatures is one of the chief difficul- 

 ties in constructing this species of achromatic lens. 



