beck's binocular dissecting microscope. 53 



(§ 19) ; and these will be found to be tbe powers most useful for 

 the purposes to which it is specially adapted. As a black back- 

 ground is often required in dissecting objects which are not trans- 

 parent, this may be most readily provided by attaching a disk of 

 dead-hlack paper to the back of the Mirror. The lenses, mirror, 

 condenser, vertical stems, and milled-head, all fit into a drawer that 

 shuts into the under-side of the Stage, and is then covered and 

 kept in place by the side-flaps ; so that, when packed together, and 

 the flaps kept down by an elastic band, as shown at b, Fig. 29, the 

 instrument is extremely portable, furnishing (so to speak) a case 

 for itself. It may be easily made to serve as a Compound Micro- 

 scope, by means of an additional stem and horizontal arm, carrying 

 alight Body. — The principal d /sadvantages of this very ingenious 

 and otherwise most convenient arrangement, are that it must be 

 always used with the light in front of the observer, or nearly so, 

 since the side-flaps interfere with the access of side-light to the 

 mirror ; and that the obstruction of the side -flaps also prevents the 

 hands from having that ready access to the mirror, which is con- 

 venient in making its adjustments.* These inconveniences, how- 

 ever, are trifling, when compared with the great facilities afforded 

 for scientific investigation by the size and firmness of the Stage, 

 combined with its extreme portability ; and the Author can con- 

 fidently recommend the instrument for all such purposes, from 

 much personal experience of its utility. 



38. Beck's and Nachet's Binocular Dissecting Microscopes. — A 

 more substantial and elaborate form of Dissecting Microscope, 

 devised by the late Mr. E. Beck, is represented in Fig. 30. From 

 the angles of a square mahogany base, there rise four strong 

 brass pillars, which support, at a height of 4 inches, a brass 

 plate 64 inches square, having a central aperture of 1 inch 

 across ; upon this rests a circular brass plate, of which the 

 diameter is equal to the side of the preceding, and which is 

 attached to it by a revolving fitting that surrounds the central 

 aperture, and can be tightened by a large milled-head beneath ; 

 whilst above this is a third plate, which slides easily over the 

 second, being held down upon it by springs which allow a move- 

 ment of 1 4 mcu i n anv direction. The top-plate has an aperture 

 of 14 inch for the reception of various glasses and troughs suitable 

 for containing objects for dissection ; and into it can also be fitted 

 a spring holder, suitable to receive and secure a glass slide of the 

 ordinary size. By turning the large circular plate, the object under 

 observation may be easily made to rotate, without disturbing its 

 relation to the optical portions of the instrument ; whilst a travers- 

 ing movement may be given to it in any direction, by acting upon 



* Another form of this instrument, supported by brass folding legs 

 instead of by wooden flaps, so as to allow the light to fall on the mirror 

 from either side as well as from the front, is made by Messrs. Parkes 

 of Birmingham. 



