190 



KNOWLEDGE. 



[AuGTIRT, 1901. 



and hours during holiday time which might otherwise be dull 

 and -wearisome, could be rendered profitalile and enjoyable if a 

 microscope were available. 



The special microscopes to which attention is directed are : — 

 The Diagnostic Microscope by C. Baker, made at the suggestion 

 of Surgeon-Major Ronald Ross, for the diagnosis of malarial 

 fever, etc. ' 



The American Portable Microscope by Bausch & Lomb, of 

 Rochester, New York, the London agents for whom are Messrs. 

 Staley & Co., Aldermanbury. 



The Portable Continental and the Portable Star Microscopes 

 by R. e*i .1. Beck. 



The Improved Clinical Microscopes by Swift & Son. 



The Portable Microscope by Watson & Sons. 



The above is practically a complete list of the portable 

 microscopes that are made, excepting only a new one by Leitz. 

 All of them have their points of advantage, either in weight. 

 size, completene.ss of mechanical fittings, or jirice. The makers' 

 catalogues will give full particulars. 



In passing I feel bound to give S|jecial mention to the very 

 neat and ingeniously made instrument by Swift & Son, refen-ed 

 to in the above list. It exactly fits my idea of a portable 

 microscope. 



Note on Examin.\tio\ of Blood. — A microscopical 

 examination of a stained specimen of pathological blood 

 implies a comparison with the ap])earance of normal blood 

 when subjected to the same staining process. The experienced 

 observer unconsciously makes use of his mental picture of the 

 normal specimen in doing this work, and to him it is sufficient. 

 In fixing and staining blood-spreads, however, a slight variation 

 in technique may produce a decided difference in results, 

 consequently those who have had comparatively little experience 

 in such work will find it difficult to secure uniform results 

 without a considerable laboratory equipment. In preparing 

 pathological specimens in such cases a spread of normal blood 

 may. at the same time, be subjected to the same technique and 

 mounted on the slide with the pathological specimen, making 

 exact and reliable comparison a very easy matter. Dried 

 blood-spreads can be kept indefinitely, so a supply of normal 

 specimens can easily be held in constant readiness for use. 



NOTES AND QUERIES. 



E. A. .lonex. — I am sorry I cannot direct you to a source for 

 PalcKolithic flint implements, but if you were to communicate 

 with JMr. T. Russell, of 78, Newgate Street, he would no doubt 

 be able to put you in the wa}' of obtaining them. 



W. P. Williams. — A micro-scope suitable for general purposes 

 and for the study of rocks and minerals need not be of special 

 construction. It should have a stage that rotates concentrically, 

 and this ought to be provided with screws so that it could be 

 centred to any objective, or alternatively, a nosepiece with 

 centering screws to attach to the lower end of the microscope 

 tube and receive the objectives. You would need a polariscope ; 

 the polariser should have its rotating circle divided and a con- 

 denser system attachable over the prism to come flush with the 

 / surface of the stage. If you already have a substage condenser 

 of large aperture, the ])olariser could be arranged to work with 

 that. The analyzer would probably be found most useful if 

 mounted over the eyepiece, and this also could have a divided 

 circle attached to it. Extra fittings for petrology, such as a 

 calcspar plate, Bertrand's lens, etc., would be applicable to an 

 ordinary microscope equipjied as above. If I can aid you 

 further I shall be glad to do so. 



Communications and enquiries on Microscopical inafters are 

 cordially invited, and, shonld he addressed to M. I. CliOSS, 

 Knowledge Office, 326, Hi(ih Holhorn, W.C. 



NOTES ON COMETS AND METEORS. 



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



Naked-eyk Comkts. — These objects ccrtaiiilv :i|>)i('in' inni-r cil'li'ii 

 than is gencnilly .supposed, bift the circ'iimstauc-es arc luifavciimihlc 

 and the apjiaritions brief. A conspieuoiia (^omet i.s rarely prpsontod 

 tinder the best conditions, but when these ooriir, the sticclacle is lout; 

 ivnienibered as one of special intei'est. Amon^ tliosr conii'ts wlucli 

 were well exhibited from un obscrvalioiial |)oirit of view in:iv be 



instanced Donati's 1858, Coggia's 1874, Tebbntt's 1881, so. Certain 

 other fiiu! comets were seen by few persons, and have now almost 

 entirely passed out of memory owing to the dilliculties which attended 

 their observation. On an average, a comet is visible to tlie naked eye 

 UTnumlly, for since the beginning of 1880 mor^ than 20 of these 

 olijtM'ts liave been recorded, the list ijeing as follows: — 



Yi-iir. Month. Comet. 



1880 Ki'lirniiry Great southern conn't, tail 411". 



ISHO Octolier" Hartwig. 



1H8L .Tune-September ... Tebhutt. fine comet, tail 15"". 



1881 Julv-Aunust ... Scliacbt-rle, tail 10^ 



1882 Ma'v-June Wells. 



1882-.3 October-February ... Great comet, tail 22". 



188.3-4 November-JanuaVy Pons (1812). 



1881) Ajiril ... "... Fabrv. 



1886 May Barn'ard. 



1881) No\ ember-December Barnard. 



1887 January ... ... Great southern coiucl, tail 35". 



1S88 April-Mav Sawertlial. 



18S0 .July... ' Davidson. 



1892 April-May Swift, tail 20°. 



1892 Noveinbcr Holmes. 



189;i .Tuly Quenissett. 



1893 October Brooks. 



1894 April-May Gale. 



189.5 Noveniiier-f)eeenil)er Perrine. 



1899 Mar<-li-Miiy Swift. 



IflOl April-May ... ... Great southern comet, tail 1.5°. 



The tal)lc might be increased by the addition of several other coniets 

 which were Just visible to the naked eye, but in the historical records 

 of these lutdies details are not always given on this point. 



The Great SonTHEBjj Comet. — This object has now passed 

 beyond the reach of the most powerful telescopes. lliere seems, 

 however, a possibility that it may be re-detected in the early autumn, 

 though the prospect is not an inviting one, the comet being situated at 

 a I'onsidcrablc distance from the earth. 



Comet Gale (1894, II.). — Definitive elements have been computed 

 by Mr. 11. A. Peck, fi'om more than .500 observations extending o^er 

 the interval of 141 days, from April 2 to August 21. The orbit proves 

 to be ellijitical with a period of 1143 years. The elements agree very 

 well with those derived by the Rev. Dr. Roseby, from observations 

 during 78 days which indicated a period of lOOL years. 



Encke's Comet. — This interesting object returns to perihelion in 

 September, 1901, but the conditions will not be favourable, and the 

 comet is not likely to be, much observed. At the time of its passage 

 through penhelidn it will be on the opposite side of the sun to the 

 earth. This comet was first discovered by Mecbain, at Paris, in 1786, 

 and at later returns by Miss Caroline Herschel, iu 1795, by Thiilis, in 

 1805, and by Pons, in 1818. Encke soon afterwards determined its 

 real orbit and jjrcdictcd its retmai in 1822, wliich duly occurred. 

 Since 1822 tbe comet has made 21 returns, each of which has been 

 observed. 



August Meteoes. — The moon will interfere with observation early 

 in tbe month, but meteors are nsnally so numerous at this eijoch that 

 the observer may gather plenty of materials even in a l)riglit sky. At 

 the time of tbe maxinunn (August 11), and during the later stages of 

 the shower, the circumstances will be more favourable, and with fine 

 weather the display may he well observed. Tlie ])aths of all tbe 

 brighter meteors seen should be recorded, and especially those which 

 belong to the minor streams. In every case it is desirable tliat the 

 direction of Jlir/hf should lie noted with the utmost care and precision, 

 for it is cntirclv u])ou this feature that the accuriu^y of the radiaut ])oiut 

 ilcpeniis. Tbe visifilc ibo'ation of the Perseid shower probably extends 

 to tlie end of the third week in August, but it is extremely difficult to 

 assign the definite limits. In 19(X), the w riter at Bristol saw a radiant 

 of swift, streak-leaving meteors on August 22 at 59" + 59", which 

 corresponds with the probable place of the Perseid radiant on that 

 date, but there is a persistent shower of Canielopardids from tbe same 

 ap})arent position during August, and it is therefore ilonbtful whether 

 the meteors annually seen on about August 21 and 22 are really late 

 members of the great Perseid display. Observations should l)e made 

 between August 17 and 22 with a view .to obtain moi'e evidence on tbe 

 point. 



Bright Meteor. — On July S a meteor, moving very slowly and 

 with an extremely long path, was observed at Torquay by Miss L. M. 

 Milner, and at Kastbourne by Mr. H. M. Whitley. At Torijuay tbe 

 object passed from a /3 Capricorni to Aries, while at Eastbourne the 

 observed course was from f- Serpentis to Cor Caroli. Tlie radiant was 

 at 253" — 24°, so that it belonged to the .Tune -July Scorpiids. At 

 Eastbourne the meteor was as bright as Jupiter, and its duration was 

 10 seconds. It fell from heights of 53 to 2t) miles, and its velocity was 



