179 



The base is of black walnut, supporting an upright flat portion of 

 the same wood, with two crotches in which the somewhat heavily- 

 loaded tube rests, inclined at an angle of thirty degrees from the 

 horizontal. The adjustment is by rotation of the large shade disc, 

 a pin projecting from which rests against the slightly-inclined 

 extremity of the upright support, and is according to the general 

 plan long employed by him. The stage is of iron, eight inches 

 long, and rests against the flat ends of a horse-shoe magnet. It 

 turns on an edge a little to the left (or right, if preferred) of the 

 middle, so that the up and down motion is a radial one, while the lat- 

 eral motion is sliding. An achromatic condenser and diaphragm of 

 the simplest construction are brought close to the stage. The direct 

 light of a kerosene lamp, which is brought as near as possible to the 

 achromatic condenser, is preferred for illumination. When daylight 

 is used the following is the arrangement : A plano-convex lens is 

 mounted in a deep, open frame, and may be thus used as a magnifier 

 or a bull's-eye. When a reflector is wanted, two round pieces of plane 

 mirror, fastened back to back, are placed in the frame, so that one of 

 them shall lie against the plane side of the lens. This contrivance 

 gives us a plane mirror on one side, and a combination practically 

 equivalent to a concave mirror on the other. The instrument is so 

 arranged as to be very easily packed and handled. Dr. Holmes 

 claims that it is perfectly solid, simple in management, gives a bril- 

 liant and readily adjusted illumination, especially with artificial light, 

 has no machinery which can get out of order, and can be constructed 

 very cheaply. The idea of the magnetic stage is not original, but 

 the arrangement of it is new, embodying the radial movement first 

 used, he believes, by himself, in a microscopic stage. He has for 

 some years used instruments of his contrivance resembling this in 

 many points, with satisfaction, but presents this model as more simple 

 than and as effective as those he has previously employed. It is 

 specially adapted for the higher magnifying powers. 



No'oemler 19, 1862. 

 The President in the chair. 



Mr. A. E. Verrill presented a paper entitled, " Review of 

 the Polyps of the Eastern Coast of the United States, with 

 descriptions of new and imperfectly known species." 



Dr. J. Wyman gave an account of recent observations on Penta- 



