*"6 FIRST-CLASS MICROSCOPES. 



First-class Microscopes. 



52. 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 indispensable addition ; and the 

 Author regards it as 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 

 (§ 48), 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 direc- 

 tion (§ 119) ; and, in addition, because in the examination of 

 objects under Polarized light, a class of appearances is produced 

 by the rotation of the object between the prisms, which is not 

 developed by the rotation of either of the prisms themselves. It 

 is also important for the most advantageous use of the Illumi- 

 nating Apparatus, that the Sub-stage also should be furnished 

 with a rotatory movement. 



53. Ross's First-class Microscope.* — To this instrument (Plate 

 iv. ) the first place may fairly be assigned without any invidious 

 preference ; since it is the one which was earliest brought (in 

 all essential features at least) to its present form. The general 

 plan of Mr. Ross's Microscope is essentially the same as that which 

 we have already seen to be adopted in a simpler form by many 

 other makers ; but it is carried out with the greatest attention to 

 solidity of construction, in those parts especially which are most 

 liable to tremor, and to the due balancing of the weight of the dif- 

 ferent parts upon tbe horizontal axis. The 'coarse' adjustment is 

 made by the large milled-head situated just behind the summit of 

 the uprights, which turns a pinion working into a rack cut on the 

 back of a very strong flattened Stem that carries the transverse 

 arm at its summit ; a second milled-head (which is here concealed 

 by the stage -fittings) is attached to the other end of the axis of the 

 pinion (as in Fig. 32), so as to be worked with the left hand. The 

 ' fine ' adjustment is effected by the milled-head on the transverse 

 Arm just behind the base of the ' body ;' this acts upon the ' nose' 

 or tube projecting below the arm, wherein the objectives are 

 screwed. The other milled-head, seen at the summit of the stem, 



favourably known to the Author, which are constructed, not only by the 

 makers of the above, but by Messrs. Baker, Highley, How, Murray and 

 Heath, Pillischer, Ross, Swift, and Wheeler, as also by Mr. Dancer, of 

 Manchester. 



'This instrument, devised by the late Mr. Andrew Ross, has under- 

 gone very important modifications at the hands of his son, Mr. Thomas 

 Ross ; having been altogether considerably lightened, and the construc- 

 tion of the Stage having been greatly improved. 



