SCIENCE. 



placed by the genus Entomophthora ; but it is proposed 

 by Giard, who has investigated the subject recently, to 

 retain these names to designaje the asexual and sexual 

 stages respectively. These plants belong to the interest- 

 ing order Saprolegniaceae. Other species of the same 

 order are abundant on dead and living fish, cray-fish, etc. 

 They have sometimes proved very destructive to the young 

 fish in hatcheries. The species of the order are not well 

 known, although examples are easily obtained. 



J. C. A. 



MICROSCOPY. • 



Mr. Julian Der'.iy recently read before the Quekett 

 Microscopical Club a paper describing various special 

 " dodges," which may be employed by microscopists to 

 facilitate their reseirches. 



I. When allowing all but adepts in the use of micro- 

 scope to peep through my high power glasses, I have 

 often felt a certain degree of uneasiness, not to say of 

 alarm, regarding the fate of valuable test-slides, or still 

 more valuable objectives. Many others here present 

 have no doubt experienced the same discomfort which I 

 find an easy matter to attenuate to a considerable extent, 

 by focussing from the eyepiece instead of from the coarse 

 or the slow motion. All that is needed for this is a rack 

 and pinion to the eyepiece of considerable length. An 

 inch or two up or down corresponds here to a fraction of 

 a turn of the fine adjustment of the microscope, so that 

 very little danger exists of any sudden contact with the 

 covering glass. As soon as an indistinct view of the 

 object is obtained through the ordinary coarse adjust- 

 ment of the microscope body, the focus is brought to 

 exactness by means of the coarse motion of the eyepiece 

 without much difficulty. For demonstrations or exhibi- 

 tions in public, microscopes could thus be made without 

 the ordinary fine motion. 



II. When mapping with micro-spectroscope, the diffi- 

 culty of measuring exactly the position of fine lines or 

 absorption bands is often great, even when using the ad- 

 mirable micrometers invented by Mr. Browning and Mr. 

 Sorby. I find that in most practical cases the micro- 

 spectrum can be thrown upon a sheet of white paper by 

 means of an ordinary camera, lucida placed over the 

 eyepiece of the spectroscope. Strong light by means of 

 a condenser has to be thrown through the liquid under 

 examination. By means of an ivory rule, finely divided, 

 and brought back to a known line, say D, all other lines 

 or bands may be directly measured off on the rule, and, 

 if desired, the exact results in millionths of a millimetre 

 may then be computed by any of the known interpola- 

 tion formulae, such as are given in Suffolk's useful little 

 book. 



III. The arrangement of small microscopic objects, 

 such as diatomis, foraminifera?, etc., on slides in regular 

 lines, circles or patterns, can be much facilitated in the 

 following way : " Draw with a pen and ink cross lines, or 

 circles, or any other figure required on the surface of the 

 plain mirror of the microscope ; then focus down until 

 the image of these lines is seen on the upper surface of 

 the top lens of the condenser. By means of a mechanical 

 finger, or of a steady hand with a rest, no difficulty will 

 now be experienced in placing the objects in perfectly 

 regular order. 



IV. I now obtain excellent condensed monochromatic 

 light by means of a bull's eye of unusual external shape, 

 the internal portion of which, however, is filled with gly- 

 cerine or oil of cloves colored to suit. This bull's eye 

 has a plane back and a concavo-convex front, and the 

 liquid is introduced through a hole in the flat side, closed 

 by a small ground stopper. This apparatus is furnished 

 wi h universal motions, and has a rack and pinion foot. 

 It was made for me by Mr. J. Browning. When using 

 blue light, produced by ammonia sulphate solutions, 1 

 have resolved, by means of this monochromatic bull's- 



eye amphipleura, with objectives in my possession, which 

 will hardly show PI urosigma angulation under ordinary 

 condenser illumir aticn. 



(@) | 



— J- LI — 1 



V. Some time ago, Mr. J. E. Ingpen, on my behalf, 

 made a communication to the Club in regard to a grow- 

 ing regard to a growing slide I had devised for some 

 special researches I was following at the time. Some 

 difficulty seems to have been found in the making of 

 these slides, so that it is with pleasure I now offer a still 

 niore simple contrivance for obtaining the same results. 

 Here is the receipt: Take an ordinary glass slip with a 

 circular hole, say, half an inch or more in diameter in 

 the ni'ddle ; lay this slip on an ordinary glass slide, not 

 perforated. Then grease the top of the upper or perfor- 

 ated slide just a little way around the circular hole, and 

 join the two slips of glass by means of two rubber rings 

 (see Fig.). The object is then placed on a thin cover- 

 glass, somewhat larger than the hole in the slide: it is 

 covered by a thin glass cover, %'m. in diameter; the 

 whole is then turned down and fastened to the slide by 

 the adherence with the grease, while the small cover pre- 

 vents the running of the liquid. The plant or animal 

 under exanvnation finds itself confined in a sort of mina- 

 ture Ward's case. When not under observation, the 

 growing slide is laid flat in a shallow plate with water 

 just above the line of junction of the two slips of glass, 

 where, by capillarity, it creeps up to the central cell, 

 where evaporation keeps the contained atmosphere in a 

 state of constant and healthy saturation. 



VI. Copal Varnish. I find this varnish dries very 

 rap ; dly if slightly heated, or even if placed on a 

 previously warmed slide. I have many hundred slides 

 of diatoms prepared in copal varnish, and my friend, 

 Mr. Van Heurck, of Antwerp, who was the first to 

 use this materia], his many thousands. The varnish 

 to be used is what is called the " pale copal," and 

 iis consistency ought to be that of oil. It is much 

 pleasanter to use than Canada balsam, does not make 

 bubbles, and its refractive index is not very different from 

 that of balsam, and does not interfere with the solution 

 of diatom markings. I have of late made many prepa- 

 rations in copal, dispensing with the cover-glass alto- 

 gether. The drop ot copal is placed on the diatoms and 

 heated lightly over the spirit-lamp. It soon takes the con- 

 sis'ency of amber, and is hard enough to sustain wiping 

 and brushing with a soft brush with impunity. The op- 

 tical aberrations produced by the cover-glass are thus 

 done away with. 



ASTRONOMICAL MEMORANDA. 



Professor C. A. Young has examined the 70 lines given 

 on Angstrom's chart as common to two or more sub- 

 stances. Of these 70 lines, 56 were seen distinctly double, or 

 triple ; 7 single ; and in regard to the remaining 7 there is 

 still an uncertainty. The instrument used was a diffraction 

 spectroscope with collimator and observing telescope, each 

 of 3-inch aperture and about 42 inches focal length, and a 

 Rutherford grating of 17,300 lines to the inch. The ap- 

 paratus was strapped to a 1 2-foot equatorial provided with 

 a driving clock, and powers magnifying from 5° to 200 

 diameters were used. A large prism with a refracting 

 angle of 20 was placed between the object glass of the 



