1ST, 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



(2j Eye-pieces and Objectives. 



The Jena Optical Glass.* — Mr. J. Swift states that the difficulties 

 in the practical use of this glass has been great, " for nearly the whole 

 of the new glass purchased by him was found to be worthless, so rapid 

 was tho deterioration of most of the samples ; and some systems of 

 lenses made of them became pitted on the surfaces within a week after 

 the manufacture. He found about three stable samples in the whole 

 of a very large batch." Figs. 74 and 75 repi'esent in the actual dimen- 

 sions the eye-piece and objective of a Microscope made entirely of the 

 new materials. In fig. 74, A, B, and C are of the new crown glass, 

 and D of tho new flint. In the objective, fig. 75, A is the aperture 

 above the compound lens BC; B is of hard crown, C of flint, D crown, 



Fig. 74. 



E flint, and F a plano-convex crown element of deep curvature, cemented 

 to the meniscus flint element above it. Although it is difficult work to 

 make an objective entirely of tho new glass in its stable forms, Messrs. 

 Swift use the glass now in all their Microscopes to some extent for 

 objectives varying from the 1/12 in. immersion to the 3 in. ; the benefit, 

 they state, is that the 2 in. objective which formerly had an angular 

 aperture of 15°, with the new glass has an angular aperture of 22°, and 

 strange to say, instead of being dearer it is cheaper, because with the 

 good samples of the new glass the manufacturing optician is more sure 

 of his results. As regards the eye-piece, fig. 74, Mr. Swift says: — 

 " It would be very difficult to use the ordinary Huyghenian eye-piece of 

 the same power, as the loss of light would be so great that the detail the 

 objective would be capable of picking up would not be seen, or the eye 

 would have to be nearly in contact with the eye-piece, to enable the 

 object to be seen, but with the eye-piece shown the focal distance is so 

 increased that it can be used with as much ease as one of the ordinary 

 construction with a magnification of only ten diameters." 



Babsch, E.— Society Screw. 



[Condemns the ambiguity of the instructions of the original committee, and 

 urges that something should be done to get a better standard.] 



The Microscope, VIII. (1888) p. 127. 



The Engineer, 1888, March 2, pp. 182-3 (2 figs.). 



