SCIENCE-GOSSIJ\ 



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" IIoloscopk" EvEi'iBCBs. — These eyepieces 

 ate an entirely new departure, anil ime on which we 

 can conjjratulate the makers. They are designed to 

 wiirk with the apochronialic olijcctives, and possess 

 the so-called "over-correction" necessary for that 

 purpose, but by means of an inner adjustable draw- 

 lube the eyepiece corrections can be varied at will 

 until actual "under-correction" is reached. It 

 follows therefore that these eyepieces can be used 

 with ordinary achromatic objectives also, thus saving 

 the necessity of having two sets of eyepieces. This 

 means of adjustniciU has a further advantage, in 

 that it enables the eyepiece to be adjusted to any 

 individual objective, very few of the apochromatic 

 series being identical in the amount of their under- 

 correction. The drawtubc is graduated to enable the 

 degree of extension to be noted. We have had an 

 <ipportunity of examining these eyepieces, and find 

 them in every way satisfactory — they give a most 

 brilliant image ;mii1 .Miui-iic definition. The 



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makers, Messrs. \V. Watson and Sons, of High 

 Ilolborn, have so arranged them that they all work 

 in approximately the same focal plane, and instead 

 of the too-customary arbitrary numeration or letter- 

 ing, each eyepiece is marked with its magnification 

 at a certain tube length. Messrs. \\'atson have, we 

 think, gone rather beyond the requirements of the 

 case in marking the large-size eyepieces 7, 10, 14, 

 and 20 for a /o huh tube, and the small-size or 

 " Student's " eyepieces 5, 7, 10, and 14 for the 6 inch 

 tube. As the eyepieces can of course be used for 

 either tube length, we think this likely to prove con- 

 fusing. The price of the " Student's " size eyepieces 

 is 17s. 6d., and of the large and capped size 22s. 6d. 



" IIoLOSCOric " OiijECTivES.— Messrs. Wat.son 

 have also sent for our inspection the first two of 

 a new series of achromatic objectives, in which, as 

 they themselves say, a very remarkable degree of 

 aplanatism is attained. To obtain this an entirely 

 new formula has been resorted to. The corrections for 

 spherical aberration are effected by means of a triple 

 back lens, and the objectives have the same correc- 

 tions as the apochromatic objectives, and require to 

 be used with compensating eye-pieces or « ith the new 

 " Holoscopic " eye-pieces mentioned above. The 

 lenses sent us were the 12 mm. {'lin.) N..\. '45- 

 and the 6 mm. (|in.) X.A. 74. Both are really 

 excellent lenses, flat in the field, of exquisite defini- 

 tion, bearing high eye-piecing well, and though of only 

 comparatively moderate aperture, passing an unusual 

 amount of light. The 6 mm. sent us, being an early 

 lens, was, however, deficient in working distance, but 

 the makers state that this has now been rectified. 

 The lenses are made for either the 6in. or loin, tube, 

 and on each lens is marked not only the so-called 

 focal length, but the tube length for which the 

 objective is corrected, and the N.A. ; this last and 

 the magnifications being exactly stated and guaranteed. 



The price of either len.s is £z los., and the makers 

 have other ixjwers in hand. They are anxious to 

 afford every facility for examination and coni|>arison 

 of the.se new objectives. 



Microi'Hotoi;k.vi'Iiy with okihn.vrv Ca.mkras. 

 — Messrs. J. H. and K. A. Harbour, of Hangor, Co. 

 Down, have sent us micro-photographs of the spores 

 and sporangia of a fern, also of the hairs and scales of 

 the wing of a butterfly. These were taken with an 

 ordinary Lizar's \ plate " Challenge" camera, I'agel's 

 dry plates, slow, and a round w ick reading lamp. The 

 microscope alsci was a non-inclinable one, and 

 re(|uired propping up with books in the necessary 

 horizontal position. The camera lens was removed 

 and the connection between the aperture and the 

 microscope tube was made by means of a black cloth, 

 the image of the object being, of course, focusscd on 

 the glass screen. A ten minutes exposure was given, 

 and the paper used was Ilford I'.tJ. I'. We have 

 mentioned these particulars at length, with a view to 

 encouraging other beginners to make similar first 

 attempts, and to remind them that much may be done 

 with very ordinary apparatus. 



Dendritic Ckystai.s in I'ArER. — We shall be 

 grateful to any of our readers who can send us any 

 specimens of the above, stating, if possible, where 

 found arid the approximate age. 



ANSWERS TO CORRESPONDENTS. 

 Books o.n Microscoi'V. — T.M. (Manor Park, E.) 

 (l.) Cross and Cole's "Modern Microscopy" gives 

 full details, suitable for beginners, as well as advanced 

 students, as to mounting. Davies' book is less con- 

 venient and less simple- (2.) Hy. Scherren's " Ponds 

 .ind Rock Pools"' is good, so is Sl.ick (see S.-G., \'ol. 

 vi., N.S., p. 57 and ante, 173). There are also little 

 books by Butler and Simpson in "The \'oung Col- 

 lector Series." (3.) Kent's "Manual of the Infusoria" 

 is a standard authority — 3 vols., with plates, worth, 

 second-hand, about 50s. Pennington's " Natural 

 History of British Zoophytes" (los. 6d.) is useful. If 

 you are particularly interested in Desmids or Diatoms I 

 will name books dealing with these subjects. (4.) I am 

 sorry I have no notes about the Wanstead Ponds. 

 The Richmond Ponds are alluded to in Scie.nce- 

 Gossii', vol. vi., pp. S6 and 156. 



MicROsconc'M.XTERiAL. — T.W.B. (Old Charl- 

 ton). The only persons I can suggest other than 

 those you name are Mr. F. P. Smith, of Islington, or 

 Mr. Abraham Flatters, of Manchester. Both adver- 

 tise in SciENCE-Gossir. There is a series of 48 

 different preparations put up ready for mounting in is. 

 packets, that can be obtained at any microscopical 

 optician's : but if you want specific objects like insect 

 eggs, I would suggest advertising in the Exchange 

 Column of SciENCE-GossH', when you should have 

 no difficulty in obtaining a satisfactory- response. 



V.T. (Chorley). — .Mr. C. F. Rousselet, to whom 

 we sent your i|ueries, has kindly answered them as 

 follows: — The rotifer is Aniiiaca so nilala, a well- 

 known but not very common species. The sketch is 

 not quite correct, n<ir is it right to say that it lives 

 in its lorica much like iffUicrla does in its tube. 

 The latter is a structure built round the animal's body 

 for protection, whilst the lorica of Auurcua is the 

 hardened integument, or outer skin of the rotifer, 

 organically connected with its body. I am much 

 inclined to think that the pink bodies are the broken- 

 up granular Zoocytium of the flagellate infusorian 

 Spongomonas saciuliis, which is said to be rust-brown 

 in colour when living. See Saville Kent's " Infu- 

 soria," Vol. i., p. 28S. The fine white threads are 

 the infusorian Spirostomuin ambiguum. 



