2l8 THE HISTOKY AND DEVELOPMENT OF THE MICEOSCOPE 



Second-class microscopes are made in great variety by English 

 makers. 



One of the finest examples of this class of microscope at present 

 brought within the reach of the average student's means is that 

 known as the * Edinburgh Student's Microscope " H," ' by the firm 

 of Watson and Sons. It is the most complete of a series of similar 

 stands varying in cost and completeness. It is illustrated in 

 fig. 173, where it will be seen that it has the first prime requisite, a 

 rigid foundation combined with lightness a tripod having a spread 

 of 7 inches and it is also possessed of a well-constructed mechanical 

 stage which is built with the instrument, an advantage over the 

 best 'attachable' stage. 



It is essentially a student's microscope, and although of so low a 

 price is not only a specimen of the best workmanship, but is also 

 extremely complete and represents an advanced type of construction 

 capable of doing all ordinary and much experimental work. 



Belonging to this class is an instrument by Baker known as 

 his Model, No. 2. It is smaller than the 'A' stand of the same 

 type and is simplified, but is capable of doing the most refined and 

 critical work. It is illustrated in fig. 174. The coarse and fine 

 adjustments are the same. The mechanical stage has rectangular 

 movements of one inch ; the Turrell arrangement is not adopted ; 

 but the whole stage can be rotated through an arc of 300. The 

 sub-stage has diagonal rack and pinion focussing movements with 

 centring screws, and can be supplied with every improvement 

 applying to the adjustment of the sub-stage. Taking this instru- 

 ment as a whole the thoroughly practical character of the model, 

 the high quality of the workmanship, the fact that it will take all 

 the optical apparatus of the best model, and that all fittings are 

 sprung and possessed of adjusting screws to compensate for wear 

 we have in this microscope one of the very best of its class. 



Powell and Lealand make an instrument of this class, having 

 a quality of work not second even to their large stand. It is 

 illustrated in fig. 175. The tube length is the same, but the stage 

 and the foot are smaller than in the large instrument. There is 

 no rotary movement to the sub- stage, and its centring is done by 

 the crossing of sectors and not lines at right angles ; but this is in 

 no way a defect. All the movements and adjustments are other- 

 wise as in No. 1. 



Baker, of Holborn, makes a very admirable and useful instru- 

 ment of this class known as his D.P.H. microscope, No. 1. It 

 has a diagonal rack and pinion coarse movement, a micrometer screw 

 and lever fine adjustment, giving a movement of 3-^5- of an inch for 

 each revolution of the milled head ; a draw- tube, every 10 mm. of 

 which is engraved with a ring, extending to 250 mm. and closing 

 to 150 mm., thus allowing the use of either English or Continental 

 objectives ; it possesses a mechanical stage giving a movement of 25 mm. 

 in either direction, graduated to ^ mm. ; the milled head of the trans- 

 verse motion is below the level of the top plate, and as the other is 

 removable large culture plates can be examined, the distance from 

 optic axis to limb (2^ in.) allowing of their easy manipulation ; the 



