40 Modern Microscopy. 



plished. This glass is now obtainable by any optician, and 

 the apochromatic objectives are made in great perfection by 

 many other firms, notably Eeichert of Vienna, and Powell 

 and Lealand of London, whose productions compare favour- 

 ably with the best of the original firm, Zeiss. Now, these 

 lenses are very expensive, and quite beyond the reach of the 

 ordinary amateur who, taking up microscopy apart from 

 its scientific aspect, endeavours to find his recreation in the 

 minute, and excepting to a trained critical eye they would 

 not be found to possess the extraordinary merit that is 

 claimed for them, and the question naturally occurs, ' Is it 

 worth while paying four times the price of a good high-class 

 achromatic objective for an apocliromatic objective and the 

 incident extra cost of eyepieces ?' In reply, we would say, 

 ' Yes ' and ' No.' Yes, if the intending purchaser proposes 

 to do his work on the most exact and highest scale, and to 

 conduct original research ; no, if his aim is only to examine 

 into nature's small things without attempting to obtain the 

 apparently impossible in results, and the observation of 

 structure not hitherto discovered. We would here quote 

 from the words of Professor H. L. Tolman, President of the 

 Illinois State Microscopical Society : ' Of the apocliromatic 

 objectives and their comparative advantages with the 

 ordinary highest-class lenses, it must be remembered that 

 the difference in degree between the performance of the best 

 American and English achromatic lenses and the Zeiss 

 apochromatics is often only detectable by the experienced 

 eye ; and, secondly, that the vast bulk of microscopical 

 work is done with medium or low powers, where the 

 diffracting beams play a much less important part propor- 

 tionately, the image being chiefly dioptric. As to the first 

 point, the writer may even go farther, and say that it is a 

 contested point among many of the highest authorities in 

 America whether the Zeiss apochromatics have any marked 

 practical superiority. The student may rest contented, 

 therefore, that he can work for an indefinite time with any 

 good American or English lenses without losing his time or 



