THE COMPOUND MICEOSCOPE. 91 



cal and the other circular. On account of the feet folding 

 together, this microscope can be packed in a flat box, the 

 thickness of which is regulated by the breadth of the stage. 

 When more portable and less expensive stands are required, 

 the two following deserve especial notice. 



MESSES. SMITH AND BECK'S ACHROMATIC COMPOUND 

 MICEOSCOPES FOR STUDENTS. 



Fig. 1, Plate 5, represents the largest of these instruments. 

 The base is composed of brass, cast in one piece ; it stands on 

 three feet, AAA, from which proceed the two flat, upright 

 cheeks, B B, having a trunnion joint at C, on which the stage 

 and the compound body are capable of being turned. Into 

 the plate, H, is screwed a stout tube, L, upon which slides 

 another tube supporting the straight arm, M. This last is 

 ploughed out in the same manner as the arm in the larger 

 instruments, and the compound body, N, resting on the guides, 

 O, is moved up and down it by turning the miUed head, P. 

 Within the tube at L, to which also the arm, M, is attached, 

 is situated a spiral spring, that keeps the arm, M, always 

 firmly in contact with the plate, I ; against this last the fine 

 screw, K, with a graduated miUed head, presses ; when the 

 screw Is turned, both the arm, M, and the compound body 

 are moved slowly up or down, forming the fine adjustment. 

 The spring is prevented from forcing the arm, M, out of the 

 tube, L, by a stop situated just above the milled head, K, 

 which is not represented in the figure. The stage is a plate 

 of brass, about four inches long and two inches wide, having 

 dove-tail grooves, in which the frame, G, for holding the ob- 

 jects, slides up or down, it being readily moved by two small 

 handles projecting from it ; one of the ends of the frame is 

 provided with a socket, F, for the reception of the forceps and 

 other instruments. The mirror, D, is mounted in the usual 

 manner on the semicircle of brass, E, and is capable of being 

 turned on a large pin fitting into the end of the tube which is 

 attached to the under surface of the stage. 



The second microscope is constructed much on the same 



