12 VIEWS OF THE MICROSCOPIC WORLD. 



rays R E and V E, making at E a right angle with each other. By the aid 

 of the lens G V H, the image of the object is formed at S T, nearer the prism 

 than it would be if this lens was not employed. The image S T is still further 

 magnified by the eye-glass K I, causing the production of the second and last 

 image M N, seen at the distance of distinct vision from the eye. 



In Figure 5, a view of the instrument is seen with its various adjustments. 

 A B is a brass pillar surmounted by a brass crosspiece N. Upon the top of this 

 the main tube C D, of the instrument is fastened, to which is attached a smaller 

 tube E F. At the opposite extremity is a compound eye-piece H, which is 

 screwed into the end of an inner tube G, that slides easily within the main cylin- 

 der by means of rack-work moved by a toothed axle, the head of which is seen 

 at K. Eye-pieces of different powers are provided, each of which is fitted to the 

 inner tube. To the horizontal cylinder E F, a small tube L, is attached at right 

 angles, into the lower end of which is screwed an olgect-glass M, which can also 

 be readily removed, and others adjusted as different powers are required. At 

 F, within the smaller horizontal tube, the prism described in the last figure is 

 placed, which, receiving the rays from the object through the object-glass, reflects 

 them to the eye-glass at H. By the side of the brass pillar is a square bar of 

 copper O P, which is firmly fastened to the pillar, and crosspiece N, at the bot- 

 tom and top. Two brass sliding-collars S and R, are capable of motion up and 

 down the copper bar, by means of two toothed axles or pinions, the heads of 

 which are seen at V and T. 



To the first of these slides S, a mirror W, is attached, possessing motion in 

 all directions by means of pivots, and having on one side a plane and on the 

 other a convex mirror. The slide R supports a table X, pierced with an open- 

 ing in the centre immediately under M, in order to admit the light reflected up- 

 wards from the mirror. Over this opening the object to be magnified is adjust- 

 ed, placed on the surface of a slip of glass, and illumined by the light reflected 

 from the mirror below. For the purpose of illumination, either the diffuse light 

 of day or lamplight can be employed. When simple reflection produces sufficient 

 light, the plane mirror is used, but if a stronger illumination is needed the con- 

 cave mirror receives the light and concentrates it in the manner of .a convex lens. 

 Beneath the opening in the table, a plate of metal is so adjusted as to move 

 horizontally, perforated with apertures of different sizes, in order that the amount 

 of light, admitted through the opening in the centre of the table, may be modified 

 as circumstances require. The table X, is composed of three floors, one upon the 

 other, two being capable of motion in directions of right angles to each other, 

 while the third and lower one is stationary. Thus, when an observer is looking 

 through the instrument, the uppe/ floor can be moved to the right and left by 

 the screw Y, and this floor, together with the second immediately below, can be 

 unitedly moved backwards and forwards by a screw not seen in the plate. 



By this contrivance an object, when laid upon the table, is capable of being 

 moved in any horizontal direction, so that every part of it can be successively 

 brought into view. The table can be raised and lowered, in the manner before 

 mentioned, by the screw V, and the object is thus brought to that position before 



