chromatic lenses are to an increasing extent supplanting the older objectives, 

 yet there are a great many problems in microscopy that do not demand the 

 highest attainable degree of optical perfection, and in the majority of such cases 

 the older "achromatic" microscope will render as good and sufficient service as 

 ever, provided the instrument be good of its kind, i. e., skilfully and carefully 

 made. The objectives and eye-pieces of the older type have certainly this ad- 

 vantage that, thanks to their much simpler construction, really good lenses of 

 this class can be supplied at prices considerably lower than those of the lenses 

 of the new series, which are much more complicated and involve in their pro- 

 duction an extraordinary degree of manual skill. 



We should not omit to mention that all advantages derived from 

 the introduction of new glasses and the adoption of improved formulae 

 have been applied equally to the objectives of the older type. The 

 improvements thus effected are of considerable importance, especially in the higher 

 powers of the dry and immersion series, which may therefore, after the example 

 of other makers of similar constructions, appropriately be termed "Semi- 

 apochromatic Lenses". 



In our supplementary catalogue of 1886, which deals with the objectives 

 and eye-pieces of the new series, we made our first attempt at introducing a 

 rational system of designation in place of the then prevailing aimless and 

 arbitrary modes of distinction. 



Although we believe that this system is of greater practical value than all 

 previous methods of distinguishing lenses and eye-pieces by conventional letters 

 or numbers, and though we would consider its universal adoption to be really 

 a step in the right direction, yet we deemed it wiser to retain, for a time at 

 least, the old designations of our achromatic objectives and ordinary eye-pieces. 



The application of a system of designation using a conveniently graduated scale of 

 rounded numbers would in this case necessitate many alterations in the focal lengths of 

 both objectives and eye-pieces. Besides, the extensive use of our microscopes has so 

 thoroughly accustomed our numerous patrons to the old terms some of them familiarly 

 known for 40 years and more - - that any radical change in this direction might give rise 

 to considerable confusion. 



Uince 1868 all our manufacturing processes follow the system introduced 

 into our works by Professor ABBE, a system which is based upon complete 

 theoretical computation of all the constructive data previous to actual 

 manufacture. By this method it has become possible, through judicious division 

 of labour in the various stages of manufacture under competent scientific super- 

 vision, to employ a large number of operatives in the production of lenses of 

 the greatest possible perfection. 



