94. 



KNOWLEDGE. 



[April 2, 1900. 



water is always chosen as a site for the nest, and often 

 the Black and White Fantail (Ehipidura tricolor) builds 

 its cobweb-covered nest close to that of the larger bird, 

 and joins with its neighbour in driving away hawks 

 and other common enemies. Many birds like to build 

 in company, as I have frequently noticed when travel- 

 ling in the country. Even the little Acanthiza chry- 

 sorrhoa makes its nest among the sticks which form 

 the foundation of the Eagle's home (Aquila audax). 

 Five eggs form a full clutch, and they vary much in 

 colour and disposition of markings, some having a whito 

 ground and others a reddish pink. Again, in some 

 eggs the reddish-brown markings form an irregular zone 

 round the larger end, while in others they are scattered 

 all over the egg. Some eggs are elongated in shape, 

 others much more rounded, and their average measure- 

 ments are 1.18 by .82 inch. 



itttcvoscopi). 



By John H. Cooke, f.l.s., f.g.s. 



" Microscopy and Mici'0-techiii(jue,'' by Dr. Albert Schneider, 

 of the Jforth-western University, is another work which we 

 can confidently recommend to our readers. The self-explanatory 

 title enables us to disjiense with a description of its aims. It 

 embodies many facts and suggestions resulting from long 

 observation and a very varied practical experience : and it is 

 specially suitable as a work of reference for all who are 

 interested in biological research. 



Mr. C. A. Kofaid, of the Illinois Biological Station, has 

 devoted, during recent years, considerable attention to the 

 biology of the plankton ; and his investigations have shown 

 that the Henson method of collecting with a silk net, as usually 

 practised, is very faulty and likely to lead to erroneous con- 

 clusions. The leakage of the planktonts through the yielding 

 meshes of the silk, caused by their struggles and the pressure 

 of the filtering water, is so considerable as to give rise to grave 

 errors in the final computations. A considerable volume of the 

 plankton is lost at all seasons of the year, and in some instances 

 the actual catch of the silk net is but a small fraction of the 

 total present. The plankton thus lost is composed very largely 

 of minute algaj, which constitute a fundamental link in the 

 cycle of aquatic life.' To prevent these losses he now employs 

 a filter made of filter paper No. .')7.5, Schleicher and Schiill. It 

 is very free from lint, and does not easily tear when wet. As 

 the filtering proceeds, the plankton is condensed in the bottom 

 of the funnel by means of a fine spray from a hand bulb. The 

 method is very simple and rapid, and it yields from 7.'i per cent, 

 to 80 per cent, of the planktonts, as compared with 4.'> percent, 

 to 01) per cent, with the silk net The Henson method answers 

 well enough for the larger forms, such as the Entomostracu and 

 the larger Uotifeni and Pi-oto-ou, but it is (piite inadequate for 

 the retention of Meh>s/ra, Per/dbiium, D/iiobi-i/uni, Raphidiam, 

 EiifjUfia, and other of the smaller and frequently very abundant 

 planktonts. 



At a recent meeting of the Royal Microscopical Society, 

 Dr. Measures exhibited an instrument for micrography made by 

 Zeiss, having a new form of fine adjustment, which admitted of 

 the arm being made of any length without throwing any 

 weight upon the fine adjustment screw. The manner in which 

 the speed of the fine adjustment is reduced is most ingenious. 

 The motion was extremely slow, being only l-62i> in. for everv 

 revolution of the screw. The application of the principle oi 

 the endless screw is a novel way of slowing down the fine 

 adjustment. Among other advantages claimed for the apparatus 

 are the increa.sed length of arm and the reduction of weight on 

 the fine adjustment to one-fifth of that which is usually put 

 upon it. 



For histological and biological work, an Abbe sub-stage con- 

 denser is indispensable. With the condenser open a cone of 

 light, having an angle of divergence of 120'', is brought to a 

 focus upon the object. Viewed with this intense hght, the 

 delicate contours of trans|)arent objects, which are made visible 

 by differences of refraction, are almost entirely lost, and the 



stained portions of the specimens which would be, without the 

 condenser, more or less concealed by the outlines of the unstained 

 portions, stand out in bold relief. This "isolation of the stained 

 image," as Koch terms it, is of great value in histological study. 

 An Abbr condenser should be found in every histologist's 

 laboratory. 



Ground glass is a useful adjuoct to the laboratory appliances 

 of microscopist and microphotographer ; but it is not always 

 possible to obtain glass having a grain of sufficient fineness to 

 be of much use. Ground glass may be easily prepared by 

 placing some fine emery powder between two pieces of glass, 

 and then rubbing the glasses together for a few minutes. If 

 the glass becomes too opaque it may be rendered more trans- 

 lucent by rubbing some oil upon it. 



One of the principal reasons for using lacquer on microscopes 

 is to protect the metal from oxidation. Lacquer is readily 

 soluble in alcohol, and great care should therefore be taken when 

 using this reagent. The practice of cleaning the brass work of 

 the instrument with alcohol is, therefore, to be deprecated. 



NOTES ON COMETS AND METEORS. 



By W. F. Denning, f.k.a.s. 



(ii.icoBiNi's CoMKT (1900 a). — The discoverer gives paraboh.: 

 elements in Ast. Nach. 3624, from observations on January 31st, 

 I'ebruarv 3rd and 6th, The comet is now practically invisible, 

 being ext'emely faint and situated too near to the sun for .satis- 

 factory observation. Its periheUon passage will take place on 

 ^ pril 28;li, but there is scarcely a possibility that the object vnXi 

 bi- observable at this period even in very powerful telescopes. On 

 February 21st the comet was observed by Kobold at Strassburg. 

 and he describes it as 1 minute of arc in diameter, round, and be- 

 tween the 12th and 13th mag. 



In April the relative motions of the comet and earth will cause tlie 

 two bodies to begin to approach each other, and in May and June this 

 approach will be very rapid, so that in July and August the comet 

 will be much nearer the earth, and considerably brighter than it 

 was at the time of its discovery. It will also be veiy favourably 

 visible as regards its position in the sky. The following condensed 

 tphtmeris by A. Berberich (Ast. Nach. 3627) wiU exhibit the 

 varying position and distance of the comet during the ensuing 

 six months : — 



Disiance from 

 Date E.A. Dec. Earth in Millions 



IWO. H. M. = of Miles. 



April 3 ... 1 41-4 + 11 27 ... 217 

 „ 27 ... 1 3.32 + 17 28 ... 214 

 May 29 ... 190 -^ 27 7 ... 180 

 Jmie 3(1 ... 23 46 9 + 41 31 ... 128 

 Aug. 1 ... 19 .36-3 + 41 20 ... Ill 

 Sciit. 2 ... 17 39-2 + 17 50 ... 170 

 Oct. 4 ... 17 23-2 -I- 5 55 ... 251 



L.iRGE Comets. — It is now many years since we were visiteH by 

 a really large comet favourably visible in the evening sky. In Juno 

 and July, 1881, a fine comet presented itself in the northern heavens, 

 and in August of the same year Schacberle's comet became fairly 

 (tnspicuous as it passed under the well-known stars of Ursa Major 

 A brilliant comet with a tail 22 degrees long was, percejjtible in 

 the autvmm mornings of 1882. Since that year we have had several 

 fairly conspicuous comets, but not one with a position and bright 

 ness which enabled it to arrest much public attention. It is a 

 I uridus fact, to which the writer drew notice in the " Astrouomica 

 Kegister " for April, 1883, that the majority of the large comets 

 of the present century have appeared at intervals of about 19 j years. 

 There were several large comets observed in or near the vears 

 1823, 1843, 1862, and 1881. If this cycle indicates something 

 more than fortuitous agreements then we may expect to see several 

 fine naked eye comets during the ensuing few years. This should 

 be an encouragement to comet-seekers to redouble their efforts. 

 But though the cycle referred to appears to be tolerably well 

 marked it is difficult to understand how it could exist in relation 

 to bodies having exceedingly long periods, and, moreover, it 

 apparently fails in its application to the large comets of the 18th 

 century. 



DoiTELY OnsEuvKD Meteors. — On Januaiy 25th, llh. 10m., a 

 meteor of about 2nd mag. was recorded by Prof. A. 8. Herrfchel 

 at Slough, and ilr. J. H. Bridger at Farnborough. The radiant 

 was at 45 degrees plus 62 degrees, and the meteor descended from 65 

 to 44mUes over Warwickshire. On lanuai-y 27th, llh. 10m., a veiy 

 slow-moving meteor of 1st mag. was registered by Prof. Herschel 



