247 



Dr. Bacon also exhibited specimens of Foraminifera 

 and Polycistina found in deep soundings of the Atlantic 

 Ocean. 



Mr. C. L. Andrews exhibited specimens of Algae. 



Mr. Chas. K. Stevens, of Lawrence, exhibited one of 

 Spencer's microscopes, to which were adapted a second 

 set of lenses made by Nachet of Paris, and embodying 

 some recent improvements. 



A description of a new stand for the compound micro- 

 scope was given, and the instrument exhibited by Dr. 

 Oliver Wendell Holmes, as follows : — 



The more especial object of this mechanical arrangement is to 

 facilitate the use of the direct light of a lamp placed close to the 

 object. Many of our microscopists must have seen Mr. Spencer 

 use a lamp in this way, holding it in his hand and varying the 

 distance and obliquity so as to produce the particular effect de- 

 sired. The advantages of direct light are its easy management, 

 its brilliant eflPects, and the more perfect definition it gives of deli- 

 cate objects. But, inasmuch as the heat and smoke of the lamp 

 ascend, this method of illumination can only be used with the 

 microscope-tube (or compound body) in the horizontal or moder- 

 ately inclined position, unless the lamp be so far removed as to 

 lose its peculiar advantages. It is evident that the lamp cannot 

 be used at all with the tube vertical and directly over it. 



If an instrument is to be employed in the horizontal or slightly 

 inclined position, it will require a stage movement ; otherwise both 

 hands will be needed to move the object, and will even then find 

 it awkward to do so, as the object must be secured to prevent its 

 sliding. Again, if the stage is inclined, and the lamp close to it, 

 it is evident that the broader the stage the more it overhangs the 

 lamp, and the more it is exposed to its smoke and heat. By 

 making the stage open at top, like a horseshoe, we get rid of this 

 difficuhy entirely. 



An instrument that answers this special object alone, namely, 

 the use of direct light, can Ijc made, on the general plan of the 

 one I show the Society, with great ease, and at small expense. 



