206 THE HISTORY AND DEVELOPMENT OF THE MICROSCOPE 



fairly compared with equally recent American adaptations of the same 

 microscope ; and then endeavour, after examining instruments of 

 a lower class, to give a dispassionate estimate of this model as com- 

 pared with that of the highest-class English type. 



Amongst Continental makers the firm of Zeiss has taken a fare- 

 most position and has secured a well-deserved world-wide fame. 

 Their largest microscope is shown in fig. 167. It is a model of fine 

 workmanship and has been adapted with singular ingenuity to the 

 reception of all their accessory apparatus. The upper body is 

 inclinable from the vertical to the horizontal position. It is 

 provided with coarse rack-and- pinion adjustment, and fine adjust- 

 ment by means of a direct acting micrometer screw with divided 

 head. The sub -stage takes all the apparatus provided by this firm, 

 and in addition it may, by means of a small lever, be swung out of 

 its central position, * so as to facilitate rapid transition to illumina- 

 tion with the cylinder-diaphragm,' w r hile below the condenser is a 

 movable iris diaphragm fitted with a rack-and-pinion movement to 

 throw it out of the centre, and which can be rotated about the axis 

 or entirely swung out. 



The circular object stage rotates (not by rack and pinion), but 

 has centring screws. The aperture in the stage has received a 

 more oval form. The rack-and-pinion rectangular movements are 

 1^-in. vertical and 2-iii. lateral ; the milled heads are small but 

 efficient and work smoothly. That for transverse movement being 

 placed upon the top of the stage. 



Reichert, of Vienna, makes a stand which in the main cor- 

 responds with that of Zeiss, and we are enabled to speak with 

 confidence of the high quality of the workmanship ; but in illustra- 

 tion we choose not the IA stand but the large stand known as I IB, 

 an illustration of w T hich is given at fig. 168. Our object in choosing 

 this instrument is that it combines every essential of the IA stand, 

 and in addition is furnished with the new lever fine adjustment, 

 invented so recently by Reichert, and of whose value we have 

 already given our judgment. It will be seen that on the part of the 

 body which the fine adjustment milled head crowns there is a 

 protrusion on the right and left hand side of the pillar. This is the 

 only addition outwardly that the new fine adjustment makes needful. 



A very high-class microscope is made by Leitz of Wetzlar, which, 

 while it retains the principal features common to all microscopes 

 based on the Continental model, has yet qualities peculiar to itself, 

 and obtains by means of workmanship and ingenuity the most ad- 

 mirable results attainable from the model on which it is based. It 

 'is inclinable with a hinged joint and clamping lever ; and the stage 

 is provided with a revolving centring table. The mechanical stai^c 

 is the * attachable ' one already described, and the adjustment of the 

 objective is by rack-and-pinion coarse adjustment, and by a fine 

 adjustment depending on a micrometer screw provided with a 

 divided screw head. The draw-tube is furnished with a millimetre 

 scale. The sub-stage is planned on the principle of the Zeiss 

 instrument and will receive the illuminating apparatus as devised 

 by Abbe, which is worked by rack-and-pinion adjustments, which 



