21 



The principal points in the simple and inexpensive arrangement to which 

 he called attention, were the following : 



1 . Fixed wooden stand, carrying with it lamp for direct illumination, 

 objectives, eyeglasses and other apparatus. 



2. Tube supported on two forks cut in the wood; inclined at an angle 

 of 35 ; rotated by turning the shade-disk, which is 8 inches in diameter, and 

 thus regulating the focal distance by the movement of a brass check which 

 bears against an inclined surface of glass, giving a rapid and medium adjust- 

 ment. 



3. Delicate secondary adjustment, by a screw with scalloped head, placed 

 close to the thumb which with the forefinger moves the object stage. This 

 screw depresses very slightly one of two brass plates, fixed to object stage, 

 against which the glass object slide is pressed forward by two small springs. 

 This arrangement has the incidental advantages of bringing all objects to the 

 same level, and of affording protection to the thin glass of the slide. 



4. Horse-shoe magnet for fixed stage. 



5. Object stage of soft iron, 8 inches long, 1 inch and wide, adhering 

 to fixed stage by attraction, assisted by brass spring at one end, loaded 

 to keep it down, moves horizontally by sliding over an edge f of an 

 inch to the left of middle of fixed stage, and up and down in the arc of a 

 circle of which this edge is the centre. Requires but one hand for manage- 

 ment, which hand is always in position to command the fine adjustment. 



6. Achromatic condenser (or any other piece of apparatus) slides in 

 between the branches of the horse-shoe magnet. The diaphragm is directly 

 behind the achromatic condenser. 



7. A small plano-convex lens occupies one hole of the diaphragm and 

 is very useful in concentrating the rays of oblique light when that is used. 



8. Although this instrument is arranged chiefly with reference to using 

 the direct rays of a lamp without any reflection, a mirror can be substituted 

 for the lamp if desired. The following is Dr. Holmes's method of arranging 

 this adjunct. A plano-convex lens is set in a frame, to be used as a condenser. 

 Two plane mirrors of the same size are cemented back to back. This double 

 mirror fits against the plane side of the lens, thus giving a plane mirror on 

 one side and the equivalent of a concave mirror on the other. 



9. Dr. Holmes employs a simple indicator, made by sticking a portion 

 of a fine needle to the diaphragm of the eye-glass with a bit of wax. This 

 is a great convenience in demonstrations, it being easy to bring any particu- 

 lar object of examination to the point of the needle by moving the stage. 



10. A very convenient complement of the instrument here shewn, is the 

 simple arrangement shewn by Quekett (fig. 257, 2d edition) which is especial- 

 ly adapted for very low powers, for dissecting, examining the circulation, etc. 



Dr. Holmes said he would take occasion to mention a plan he had lately 

 adopted, for preserving recent preparations of soft tissues so that they could 

 be shewn day after day. It is simply laying them on a wet cloth, which is it 



