278 



SCIENCE- G OS SI P. 



characterise the bottles, and that the oil is as clear, 

 colourless, and thin as when first made, and there 

 is no indication of change in its refractive index. 

 Whiih of our English opticians will be the first to 

 put immersion oil and Canada balsam in this form 

 upon the English market 1 



Watson's New "Universal" Condenser. — 

 The faults of the ordinary Abbe condenser are. as 

 is well known, the imperfection of its spherical 

 and chromatic corrections. The former in particular 

 greatly reduces the value of the condenser for 

 critical work. With a numerical aperture of from 

 1-2 to l'-i the aplanatic aperture does not exceed 

 •(55. There have been several achromatic con- 

 densers upon the market, but their aplanatic cones 

 have but slightly exceeded the simpler Abbe form, 

 whilst the mounting has been so cumbrous as to 

 frequently interfere with the movements of the 

 mechanical stage. Within the last year or two 

 there have been put upon the market several con- 

 densers of large N.A. and almost equal aplanatic 

 aperture, but their powers have been not less than 

 \ inch, with a field accordingly too small to be 

 advantageously used with low-power objectives. 

 To Mr. Chas. Baker must be given the credit for 

 first putting in the hands of microscopists a 

 condenser with a X.A. of 1*0 and an aplanatic 

 aperture exceeding -9, and with a power of less 

 than |rd inch (see S.-G. vol. vi. p. 374). Messrs. 

 Watson & Sons, of High Holborn, have just brought 

 out a similar condenser, which they have sub- 

 mitted to us for examination. Its N.A. is 1. and 

 its aplanatic aperture is not less than -95. whilst 

 if the exact thickness of slip for which it is cor- 

 rected be used its total aperture is aplanatic. The 

 power is ^th of an inch, and the mount is very 

 compact. The corrections are excellent, and we 

 can strongly recommend this condenser for almost 

 all kinds of work and for photography in par- 

 ticular. The price of the optical part (which fits 

 into the ordinary Abbe mount) is £2 7s. 6d., or 

 with mount and iris diaphragm complete £'d> 7s. 6d. 



Charles Baker's Demonstrations of Micro- 

 scopic Manipulation. — We are glad to hear that 

 this new departure {ante, p. 153) fully justifies 

 itself, and that the attendance has steadily in- 

 creased. Eleven demonstrations have been given 

 up to the time of writing, and the total attendance 

 has been 124, giving an average of eleven. Three 

 persons attended the first demonstration, whilst 

 eighteen attended the last — an increase which 

 testifies to their value. We may remind such of 

 our readers as live in London that these demon- 

 strations are given at 244 High Holborn on the 

 first and third Fridays and second and fourth 

 Tuesdays in each month from 3 to 6 p.m., and that 

 they are free to all comers. 



MEETINGS OF MICROSCOPICAL SOCIETIES. 



Royal Microscopical Society.— 20 Hanover 

 Square, W., February 19th, 8 p.m. 



Quekett Microscopical Club.— 20 Hanover 

 Square, W., February 7th, 7 p.m. ; annual meeting, 

 February 2lst, 8 p.m. 



Manchester Microscopical Society. — Grand 

 Hotel, Manchester, February 6th, 7 p.m. ; mounting 

 section, February 20th. 7 p.m. 



Sunderland Microscopical Society. — Sub- 

 scription Librarv. Sunderland, Februarv 18th, 

 7.30 p.m. 



ANSWERS TO COBRESPONDENTS. 



F. A. H. (Epsom.) — A drop of water containing 

 the Infusoria must be put on the centre of a per- 

 fectly clean slide, and the excess of water taken 

 up with blotting-paper, care being taken of course 

 not to disturb the Infusoria themselves. Fix by 

 adding a drop of absolute alcohol, stain with 

 picro-carmine. methyl-green, Bismarck-brown, or 

 haematoxylin (some infusorians take one stain 

 better than others), wash carefully first with- dilute 

 and then with absolute alcohol, and clear with a 

 drop of turpentine or oil of cloves. Remove the 

 excess of clearing fluid. Mount in Canada balsam. 

 See also two notes on rearing Amoebae, and on 

 staining Infusoria with Loeffler's alkaline methy- 

 lene-blue in the preseut number of this magazine. 



G. E. H. (Hornsey.) — You will find the above 

 method suitable for mounting Amoebae, and 

 perhaps preferable to that suggested in vol. vii. 

 p. 372. 



W. H. (Paisley.) — " C. Verick, eleve special de 

 E. Hartnack," means simply that the maker of 

 your microscope is C. Yerick, who styles himself, 

 in addition, a pupil of E. Hartnack. I do not 

 know much of Yerick, but Hartnack was a well- 

 known maker of high repute in Paris, whose 

 microscopes and lenses have had great influence 

 on microscopical progress, and whose business is 

 still carried on by MM. Nachet et Fils, Paris. 

 1695 is most certainly the number of the rnicro- 

 scojse, not the date. If it were the latter the 

 microscope would be worthy of a place in the 

 collection of the Royal Microscopical Society. 

 The data you give me are not enough for me to 

 say whether your microscope is a good one or not. 

 Has it a sub-stage condenser and good coarse and 

 fine adjustments, showing few signs of wear ? Is 

 the screw in- the bottom of the body-tube the 

 R.M.S. universal gauge, so as to take modern 

 objectives ? If so your microscope is probably a 

 good working instrument ; but microscopes and 

 objectives have undergone such great improve- 

 ment during the last decade or so that an old- 

 fashioned microscope is of little value in most 

 cases. 



[For further articles in this number on Micro- 

 scopical subjects, see pp. 260. 264. 272. and 287.] 



EXTRACTS FROM POSTAL MICROSCOPICAL 

 SOCIETY'S NOTEBOOKS. 



[Beyond necessary editorial revision these notes 

 are printed as written by the various members. — 

 Ed. Microscopy, S.-G.] 



The slides contained in this box [sections of 

 stems] will hardly commend themselves as micro- 

 scopic objects to the members of the P. M.S. They 

 are intended as illustrations of the varieties that 

 vegetable tissues take under the varying conditions 

 of exposure to light, heat, and moisture, etc. Begin- 

 ning with sections that illustrate the normal forms 

 of the monocotyledon, the dicotyledon, etc.. there 

 follow modifications of these, some of which it 

 would be difficult to assign to any of these groups 

 did there not exist other means of classification than 

 that of structural arrangement. To attempt to 

 give any special notes on such a trite subject as the 

 structure of vegetable tissues would be an insult 

 to the members of the Society, so I send my 



