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IX. — On a Means of obviating the Reflection from the inside of 

 the Body-tubes of Microscopes, ivith Suggestions for Standard 

 Gauges for the same and for Suhstage Fittings, etc. By J. W. 

 Groves, F.R.M.S., Demonstrator of Physiology in King's 

 College, London. 



(_Eead Mth January, 1880.) 



I WISH to draw the attention of the Society to a defect common to 

 all Microscopes, but which attains its worst development in the 

 instruments made on the Continent. I refer to the fact of the 

 inner surface of the body-tube acting as a reflector, due to the 

 black lining being either imperfectly put on or subsequently 

 rubbed off. In instruments of Continental manufacture the former 

 cause prevails as a rule, while in English stands, even the best, it 

 will be found that the inside of the tube, soon after, if not at the 

 time of purchase, is more or less bright for a certain distance from 

 the top, corresponding to the length of the lowest or A eye-piece. 

 When the latter is used the best performance of the Microscope is 

 obtained, all the bright reflecting surface being covered ; but when 

 higher oculars are required, then, as their tubes are shorter, there 

 remains an exposed bright surface, which reflects the light to the 

 eye, producing more or less blurr, which is sometimes so marked 

 that the higher eye-pieces become useless. I there- 

 fore propose a very simple alteration in the body- 

 tube, which would entirely do away with the defect. 



The body-tube x\. B,Fig. 14, should have inserted 

 in it a short piece of tube, A C, of the same dia- 

 meter as the eye-piece, but only as long as the 

 one of highest power. The other eye-pieces would 

 then bo in contact only with this sliort tube, as 

 shown in the figure, and the black lining of the 

 body-tube would not be rubbed, and would there- 

 fore remain uninjured. 



While suggesting an alteration in the tute, 

 I should like to bring forward a subject in regard 

 to which opticians could confer an immense boon 

 on workers with the Microscope, viz. by adopting 

 certain standard sizes for the lengths and diameters 

 of the body-tubes, substagc fittings, iVc. At present the eye-pieces, 

 condensers, Sec, of one maker will not fit the Micro.scopes of other 

 makers without special adapters ; whereas, if certain standard 

 gauges, say A, B, and C, were adopted, it would only be jiecessary 

 to order whatever might be re(j[uircd lor an A, B, or C stand, and 

 there would be a certainty of it fitting. 



VOL. III. Q 



Fig. 14. 



