44 PHOTOMICROGRAPHY 



students' microscope is non-inclinable, and fitted with 

 a sliding- sleeve coarse adjustment (Fig. 9). The useful- 

 ness of these stands is very restricted when compared 

 even with the last group, but for simple work with a 

 vertical camera they answer very well. The instrument 

 figured is by Leitz, and an excellent example of its kind. 



Comparison of Stands. If the microscopes described 

 are compared, a difference is at once noticeable be- 

 tween the English stands, on the one hand, and 

 the Continental and American stands, on the other. 

 The English microscopes are supported on a tripod 

 or claw foot, the axis on which the body swings 

 being above the level of the stage, with the consequence 

 that the balance between body and stage and substage 

 is so good that the centre of gravity always falls well 

 within the spread of the tripod, and the microscope 

 is perfectly stable in a horizontal position. The Conti- 

 nental and American stands, on the other hand, are 

 supported by a pillar rising from a horseshoe foot, 

 and the point of support is below the stage. Consequently 

 the microscope will not as a rule stand steadily by 

 itself in a horizontal position, but requires to be clamped 

 down to the table or otherwise supported. 



Another difference is found in the substage mechanism, 

 as is obvious on comparing Figs. 15 and 16 with 17 and 18. 

 There is more room between the stage and the table 

 in the ^English patterns, and the condenser is carried 

 in a ring, which is focussed by rack and pinion, and 

 bears two or three screws to centre the optical part. 

 The Iris diaphragm forms part of the condenser mount, 

 and oblique light is obtained by dropping patch 

 stops into a stop-carrier, also fitted into the mount. 

 In the typical Continental stands, as shown in Figs. 15 

 and 16, the condensing system is more compact. The 

 sleeve carrying the condenser is not usually fitted with 

 centring screws, and the Iris diaphragm is carried on 



! 



