CONSTRUCTION OF THE MICROSCOPE. & 



use for several years past, feels justified in unreservedly expressing his 

 high appreciation of it. 1 



69. Browning's Smaller Stephenson Binocular. This instrument, 

 represented in Eig. 51, is of more substantial build than the Students' 

 Binocular of Messrs, Baker ( 64); and is further distinguished by its. 

 special adaptation for use with Polarized light. In place of the reflecting 

 prism at the junction of the inclined bodies, a plane piece of dark glass, 

 silvered on one face, is hung on a horizontal axis at the polarizing angle; 

 its silvered face being turned in front when it is used for ordinary pur- 

 poses, so as to reflect into the two inclined bodies, the light-rays which 

 proceed to it from the pair of dividing prisms; whilst, when it is to act as- 

 an analyzer, it is turned on its axis by means of a milled-head so as to 

 bring the dark-glass surface to the front. Further, by fixing into the 

 arm the tube which carries the objective, with its fine adjustment, and 

 by making that which contains the dividing prisms and mirror, and 

 which also carries the double body, slide over it, the latter can either be 

 turned half round, so as to point the eye-pieces in the reverse direction 

 (for the exhibition of the object to an observer sitting at the opposite side- 

 of a small table) without any disturbance of the adjustments; or it can- 

 be lifted off altogether, and replaced by an ordinary Monocular body, 8 



FIRST-CLASS MICROSCOPES. 



70. We now pass to an entirely different class of Instruments those 

 of which the aim is, not simplicity, but perfection; not the production of 

 the best effect compatible with limited means, but the attainment of 

 everything that the Microscope can accomplish, without regard to cost 

 or complexity. To such, of course, the Stereoscopic Binocular is an in- 

 dispensable addition; and it is not less essential that the Stage should 

 have a rotatory movement in the Optic axis of the instrument; not only 

 for the due examination of opaque objects, as already mentioned ( 66) r 

 but also because this movement is requisite for the effective examination 

 of very delicate transparent objects by Oblique light, allowing the effect 

 of light and shadow to be seen in every direction; and, in addition, be- 

 cause in the examination of objects under Polarized light, a class of ap- 

 pearances is produced by the rotation of the object between the prisms, 

 which is not developed by the rotation of either of the prisms themselves. 



71. Ross's First-class Microscope. As what is known as the Ross- 

 model is still made, being preferred by some purchasers, we shall com- 

 mence with a notice of the original form of the instrument which has 

 gained so high a celebrity. The general plan of this Microscope, as 

 shown in Fig.^52, is carried out with the greatest attention to solidity of 

 construction, in those parts especially which are most liable to tremor, 



1 The price of this instrument in the simple form here figured, with one pair of 

 Eye-pieces and best 1-inch and l-4th inch (80) Objectives, and Condensing lens 

 on separate stand, in Case, is 14. A mechanical stage costs 2 10s. additional, 

 and the sub-stage (without fittings) 2 2s. A very ingenious 'swinging sub- 

 stage ' has been lately devised by Mr. Swift (" Journ. of Roy. Microsc. Soc.," vol. 

 iii., 1880, p. 867) for obtaining illumination of any degree of obliquity, even by 

 two pencils at once. The Condenser is made to slide on an arc-piece (as in Mr. 

 G-rubb's arrangement, 72), which is prolonged above the Stage for opaque 

 illumination; and with this may be combined a second arc-piece at right angles 

 to the first, carrying a second Condenser, which is found serviceable in the reso- 

 lution of difficult Diatom-tests. 



2 The price of this instrument, with one pair of Eye-pieces and Objectives of 1 

 inch (16) and l-4th inch (75), is 20. Any Accessories can readily be added to it. 



