AMERICAN OBJECTIVES EYE-PIECE 375 



which, so for as we have seen them (and we have examined 

 many), are excellent. Reichert's semi-apochromatic J is also a fine 

 and useful lens, and his jVinch apochromatic N.A. 1*30 has 

 qualities fitting it for use in any kind of research. 



But we confess tjhat it is a matter of most pleasant surprise to 

 us to find that the great American firm of Bausch and Lomb are 

 putting upon the English market objectives that fairly compete 

 with the above in the lowness of their price, while their optical 

 quality and mechanical work are of the best order. We have 

 examined these lenses with much pleasure ; they are from the com- 

 putations of Professor Hastings, and, considering the fact that they, 

 in all the higher powders especially, are so low-priced, their correc- 

 tions and high quality are beyotfd all praise. We would specially 

 call attention to a -inch, a ^-inch, and a ^-inch which we have 

 examined thoroughly and with approval that needs no quali- 

 fication when it is remembered that the most advanced Continental 

 opticians have not touched a lower price. 



Messrs. R. and J. Beck are making good objectives, oil-immer- 

 sion and other, and one of their T L- oil-immersions is sold at the 

 strikingly low figure of 4. 



Messrs. Swift and Son are making a large number of objectives, 

 especially apochromats and semi-apochromats, and they have long 

 striven to supply the student with high-quality lenses at the lowest 

 possible price. There can be no doubt that the whole secret of 

 success in this matter is dependent on a sufficiently large series of 

 experiments to determine on the right kind of glass, so as to produce 

 the highest order of ' semi-apochromatism.' 



Messrs. Watson and Sons have commenced the manufacture of a 

 new series of objectives based on original computations. These 

 promise exceedingly well. We have examined the V inch and the 

 J-inch. We find that their initial powers are 21 diameters 0'45 N.A., 

 and 40 diameters 074 N.A., and they depend for aplanatic results, 

 which are admirable, on a triple back lens. The objectives, we 

 believe, will be valuable as a series when complete. They do not 

 claim to be amongst the very low-priced lenses; but they claim, 

 and we believe they will possess, some of the best qualities which 

 should be aimed at in microscopic object-glasses. 



These facts are of importance to the medical student and to 

 opticians generally. By apochromatised and semi-apochromatised 

 objectives of the highest order the work of present and future 

 microscopy will be done that is inevitable. To thoroughly under- 

 stand what its very best results, theoretically and practically, must 

 be becomes the imperative aim of the optician who would be 

 abreast of the direct w T ants of his time ; and to produce the nearest 

 to these in objectives and eye-pieces at the lowest possible price 

 is, apart from all other issues, to be a direct benefactor of true 

 science. 



The Eye-piece. The eye-piece, sometimes called the ocular, is an 

 optical combination, the purpose of which is so to refract the diverg- 

 ing pencils of rays which form the real object-image that they may 

 all arrive at the pupil of the observer's eye. They have also to form 



