HAEDWICKE'S SCIENCE-GOSSIP. 



255 



was unaltered when I left. The arc described by 

 the pomts of the frost-crj'stals appeared to me to be 

 not more that 45°, and if the points were half an inch 

 from the centre of the wire this arc would represent 

 a space of only llhs of an inch, while the motion on 

 the surface of the wire would scarcely exceed Jth 

 of an inch. Supposing that tlie frost-crystals had 

 not been there, would the motion of the dark wire 

 have been perceptible at all ? It is doubtful, I think. 

 Were the two upper wires conveying messages at 

 the time, and does the electric current cause a rota- 

 tory vibration in the wires, too slight to be noticed 

 except under such special conditions ? 



Perhaps some electrician will answer this ques- 

 tion. Erederick T. Mott. 



Leicester. 



MICEOSCOPY. 



The Royal Microscopical, Society's " Uni- 

 versal Screw" tor Object-glasses, &c. — 

 There is a general complaint amongst microscopists 

 respecting the " so-called " universal screw. 1 have 

 myself felt great annoyance wlien finding that the 

 screw is not universal. Some of my friends' object- 

 glasses (having the '"'universal screw") do not 

 screw home in the nose-piece of one of my micro- 

 scopes, while others fit loosely the nose-piece of my 

 other instrument, although both microscopes have 

 been supplied by the makers with the so-called 

 " universal screw " ! Moreover, I have seen modern 

 object-glasses (manufactured since the introduction 

 of the universal screw) by one of the leading 

 opticians, having different gauges of universal 

 screw, and by another not only object-glasses but 

 adapted for analyzers, Brooke's nose-pieces, &c. 

 When using high powers with a microscope having 

 a concentric rotating stage (which is now con- 

 sidered almost a necessary addition) these variations 

 of gauge render the stage eccentric, and no doubt 

 very often the rotation of a stage is condemned, and 

 the workmanship considered imperfect, when the 

 fault lies in the inaccuracy of the so-called universal 

 screw of either the object-glass or of the micro- 

 scope's nose-piece, and frequently of both. 1 am 

 quite aware that the smallest particle of dust in the 

 object-glass screw wuU cause eccentricity, but this 

 drawback is not a permanent one ; it is bad enough 

 to have it when it occurs — there is no necessity to 

 make eccentricity both a feature and a fixture ! 

 With an universal screw, if we could not get in 

 every instance perfect concentricity when rotating 

 the stage, we should certainly approach it much 

 nearer than we do now ; of course accurate work- 

 manship being always taken for granted. Besides 

 the above inconveniences, there is another — -the 

 great difiiculty and trouble in centring achromatic 

 condensers of larqe angle of aperture with high 



powers, by different makers, having different uni- 

 versal screws. The Eoyal Microscopical Society 

 have undoubtedly conferred a great boon upon 

 microscopists by introducing the present "universal 

 screw " ; but could not an effort be made to render 

 the screw really universal by causing the Eoyal 

 Microscopical Society's gauge to be adopted by all 

 the London opticians ? Some technical and prac- 

 tical reasons may be adduced as to the difficulty of 

 making universally true the "universal screw"; 

 but, even admitting the next to impossibility of such 

 an accuracy, why then call the screw universal 

 when in reality nearly each maker of microscopes 

 in London has his own gauge of the " universal 

 screw " ? It would be also a great convenience to 

 have an universal gauge for the sub-stage fittings, 

 eye-pieces, &c., so that the apparatus of any one 

 maker should fit the microscopes of the others. At 

 present there is a great discrepancy in the diameter 

 and length of microscope - tubes and the gauge of 

 sub-stage fittings, of some makers, compared with 

 those of others. Why not make these also uni- 

 versal? — A. de Souza Guimaraens. 



Leaves of Vegetable Marrows. — The sur- 

 faces of the older leaves of this plant {Curcurbifa 

 ovifera) are studded with siliceous hairs, or prickles, 

 at the base of each of which is a bead-like circlet 

 of white bodies. When viewed with an inch or 

 half-inch objective, with strong light, they come out 

 well. They are better shown when the leaves have 

 been well dried, and they can then be plainly felt by 

 the fingers.—/. E. T. 



Amceb^. — I have found large numbers of this 

 animalcule in some yeast, evidently living under the 

 same conditions. They feed on the yeast torula. 

 Two or three could be seen enclosed in the Amceba 

 at one time. They varied in size, but increased and 

 moved about freely. I am at a loss to account for 

 their being found in such a situation. They were 

 taken from fermenting beer. — /. Abbott. 



Colouring Matter of Neottia Nidus-avis. — 

 M. Prillieux has recently contributed a memoir on 

 this subject. He states that nearly all phanero- 

 gamic plants in which chlorophyll is absent are 

 parasites ; Neottia nidus-avis, however, is an ex- 

 ception to the rule. The brown of its petals is 

 due to minute crystalline spangles, mostly stone. 

 coloured, about ten to fifteen thousandths of a 

 millimetre in length (sphseraphides ?) When the 

 leaves are treated with alcohol, ether, benzine, and 

 alkalies, or boiling water, a green colour is deve- 

 loped. If a liquid capable of dissolving chlorophyll 

 is used, a green solution is obtained, which gives 

 the characteristic chlorophyll absorption-spectrum. 

 The chlorophyll does not pre-exist as such, but is 

 apparently produced by the alteration of the above- 

 mentioned crystalline bodies. 



