22 BULLETIN OF THE 



perfect stability of the lens and the plate. In the present case, an 

 inspection of the two houses presented in the rural view, (especially 

 of the longer one near the middle of the picture,) with the curved 

 road winding between them to the right, shows that a revolving 

 camera was employed; the long sensitive plate having evidently 

 been simultaneously moved transversely in the reverse direction to 

 that of the objective. This perfect co-ordination of the revolving 

 and sliding movements could be obtained by a mechanical gearing ; 

 and the extended landscape be thus successively impressed upon 

 advancing portions of the plate — probably through a vertical slit 

 in a diaphragm immediately in front of the plate. That the core- 

 lation of movement has been very perfect is evidenced by the 

 admirable precision of every detail in the photograph. It will be 

 observed that the three men standing in different parts of the field 

 of view are one and the same individual, who has had time to pass 

 behind the instrument, and to twice take a new position in advance 

 of the moving camera. By bending the long card into a concave 

 arc somewhat more than the third of a cylinder, and placing the 

 eye at the axis of curvature,' it will be seen that the various slight 

 distortions of perspective (particularly in the houses) are com- 

 pletely corrected. 



Mr. J. M. Toner exhibited, apropos to the approaching centen- 

 nial of the surrender of Cornwallis at Yorktown, certain well pre- 

 served specimens of coins and medals of national historic interest, 

 viz: 



(1.) Bronze copy of medal given to Washington on the evacua- 

 tion of Boston. 



(2.) A bronze copy of a medal of Lafayette. 

 (3.) A bronze copy of a medal of Columbus. 

 (4.) A very fine half dollar of 1785. 

 (5.) A very fine Washington cent of 1791. 



204th Meeting. October 22, 1881. 



The President in the Chair. 

 Forty members present. 



