Illumination and Illuminating Apparatus 91 



external design by W. Watson and Sons, which they named 

 the Universal Condenser, but constructed on the principle of 

 their holoscopic objectives with a triple back lens of *92 inch 

 diameter. The aplanatic aperture of this exceeds *9, the 

 power is -^ inch. These two condensers are unquestionably 

 the best obtainable at the present day for the amateur and 

 he who does not do exclusively high power work, and, 

 although the cost is somewhat greater than that of the 

 chromatic Abbe illuminator, the additional expenditure 

 will be more than repaid by the fine work that will be 

 possible. 



There is one other point with regard to these condensers, 



PIG. 25. 0. BAKER'S ACHROMATIC CONDENSER. 



and that is that the mounting, which in the Abbe con- 

 densers was always large and somewhat restricted the 

 movements of the plates of a mechanical stage, is reduced 

 to considerably narrower dimensions, and the objection 

 referred to is almost entirely removed. Amongst high-power 

 condensers special mention may be made of Beck's oil 

 immersion, Swift's pan-aplanatic, and Watson's para- 

 chromatic (dry) and holoscopic (oil immersion). No 

 achromatic condensers of the types named can be obtained 

 from any Continental manufacturer. 



Messrs. Powell and Lealand are entitled to special 

 commendation for their early appreciation of the value of 

 condensers having large aplanatic apertures, and they were 

 many years in advance of other makers in the production 



