22 BULLETIN OF THE 



Mr. J. E. HiLGARD stated that having had occasion to deter- 

 mine the geographical centre of the United States, or the centre 

 of gravity of the surface of the country, he had ascertained it to 

 be near the Black Hills of Wyoming Territory 



Professor Joseph Henry made an oral commanication 



ON PHENOMENA OF SOUND AND EXPERIMENTS WITH TUNING FORKS: 



illustrating his statements by means of a set of resounding cavities. 



Dr. Wm. Thomson of Philadelphia communicated a memoir 

 entitled — 



ON A NEW METHOD FOR DETECTING AND MEASURING THE OPTICAL 

 DEFECTS OF THE EYE. 



( TAe substance of this communication is published under the title, "An Addi- 

 tional Test for the Diagnosis and Correction of the Optical Defects of 

 the Eye," in The American Journal of the Medical Sciences, N. S., 

 vol. lix., pp. 76-80.) 



4th Meeting. April 15, 1871. 



The President in the Chair. 



Mr. J. E. HiLGARD exhibited a chronograph of the kind devised 

 by Hippe of Neuehatel, and explained its construction. 



Gen. A. B. Eaton made a communication 



ON THE PRESERVATION OF FOODS, 



and exhibited specimens of preserved meats. 



Col. T. L. Casey communicated a Report by Capt. Chas. W. 

 Raymond, U. S. Engineers, 



ON THE RESULTS OF TRAVELS IN ALASKA AND THE DETERMINATION 

 OP THE POSITION OF FORT YUKON. 



(TAis Report is published as Executive Document No. 12, Senate, 42c? Con- 

 gress, \st Session.) 



