WITH THE MICROSCOPE. 231 



above alluded to was a one-eighth of an inch, by W. Wales and Co., 

 of Fort Lee, New Jersey. This glass is so constructed as to bring the 

 actinic rays to a focus. At the bottom of the draw tube was placed 

 an achromatic concave lens the amplifier of Tolles (of Canastota, 

 N. Y.), and an ordinary medium eye-piece completed the optical 

 apparatus. The eye-piece extremity of the microscope was thrust 

 into one end of a long camera-box, the connection made light-tight by 

 means of a black silk hood, and the image received on a piece of 

 plate glass, observed by means of a focussing glass, while the focal 

 adjustments were made. As with the very long camera used, the arm 

 of the observer cannot reach the milled head of the fine adjustment 

 of the microscope, this head was grooved, and connected by a band 

 with a grooved wheel at the end of a long steel rod, the other 

 extremity of which is near the observer, who, by means of it, can 

 focus accurately with any required length of camera. There is nothing 

 peculiar in the chemicals employed, and with ordinary collodion, and 

 the high power above spoken of, from thirty to forty seconds expo- 

 sure was quite sufficient. Of the foregoing devices most importance 

 is to be attached to the employment of monochromatic light (the 

 violet end of the spectrum), and the use of an object-glass con- 

 structed with special reference to the actinic rays. Both these points 

 were suggested to me by Mr. L. W. Rutherfurd, of New York, so 

 well known by his connection with telescopic photography, who has 

 thought much, and made many satisfactory experiments in this direc- 

 tion. I believe, however, that the apparatus as above described, 

 loses some of its advantages by the use of the eye-piece which I pro- 

 pose to substitute by a lens of proper magnifying power, corrected, 

 like the object-glass, in such a way as to bring to a focus the actinic 

 rays. Such a lens is now in process of construction for further 

 experiment. The pathological photographs hitherto satisfactorily 

 executed in the Museum have chiefly been made with moderate 

 magnifying powers, twelve to fifty diameters, though some experi- 

 ments with high powers justify me in the belief that with the improve- 

 ments above described, all that is desired in this direction can be 

 attained. Among these experiments I may particularly mention a view 

 magnified about four hundred diameters, of the polygonal cells and 

 flat cholesterin tables of a cholesteatoma, which was found on the 

 inner surface of the frontal bone of a soldier who died of epilepsy in 

 the neighbourhood of Washington." 



Such an extract is enough to show the activity and usefulness of 

 the department by which it is issued, and is in the highest degree 

 creditable to those who performed the work, and to the Government 

 which sanctioned and encouraged its prosecution. 



