166 



KNOWLEDGE. 



[July, 1902. 



left hand, lay thi> razor flat and diagonally across tho prepared 

 surface of the strop, and with a slight even pressure draw it 

 back foremost, and from heel to point from left to right upon 

 tho strop, turn the razor with its back upon the strop and pass 

 it from right to left. Maintain the process as in honing, but 

 back of razor forwards. After s-overal dozen strokes upon tlic 

 jiaste side, repeat tho work upon the finishing side. Draw the 

 edge of the razor between the finger and thumb or through a 

 j)iece of elder pith. If the sharpening has been accompli.shed 

 successfully, a power of 8I< diameters u|ion the microscope will 

 show the edge as a straight unbroken line. This microscopic 

 examination is best made by laying the razor upon a sheet of 

 glass. By allowing the handle to form an angle of 4:')" with the 

 blade the edge will be |)reserved from injury ; another test is 

 to take a hair from the head, and if the razor will cut it at half 

 an inch from the fingers that hold it, the edge is good. 



TnK Use of tmk Bull's Eyk.— A correspondent sends the 

 following note with regard to the position of the bull's eye in 

 relation to the lam]) and microscope : — 



I find tliat the bull's eye has to be placed in a different posi- 

 tion when an ordinary round glass chimney is used to that when 

 a metal chimney witli a flat slip of glass is employed. This is 

 probably due to the action of the plane and curved surfaces of 

 the chimneys, and can easily be proved by attaching a piece of 

 tissue paper to a slide ; this should then be placed on the stage 

 and the image of the flame focussed through the substage con- 

 denser on the tissue paper. The bull's eye should then be set 

 at the best position, the effect being watched on the tissue 

 paper. Now, if the chimney be changed, it will be observed 

 that an alteration of about i inch in the position of the bull's 

 eye will be rendered necessary. 



To fill the field of a low-power objective with light when 

 using the bull's eye and substage condenser and an ordinary 

 glass chimney with shade, the best results are obtained as 

 follows : — 



The bull's eye should be placed at its focal length from flame, 

 and the distance from flame to mirror should be three 

 times the focal length of bull's eye. When using the micro- 

 scope horizontally without the mirror, the distance from the 

 flame to the substage condenser should be four times the focal 

 length of the bull's eye. 



For instance, if the focus of the bull's eye were 2|'' in the 

 former case, the distance to the mirror would be 8f " from the 

 flame, and in the latter case the substage condenser would be 

 Hi" from the flame. 



It should be remembered that the plane side of the bull's eye 

 should be set towards the flame. 



Mr. W. Mence. of Ouse Villa, St. Ives, Hunts., kindly offers 

 to send a limited number of tubes of Melicerta rhif/ens on 

 receipt of bottle and postage, and would be glad to have 

 samples of Mycetozoa in exchange. 



NOTES AND QUERIES. 



A. Vit;ar. — Diatom slide, with list of names and comments by 

 the gentleman who kindly .acts as consultant for this depart- 

 ment, has been returned to you by post. 



E. E. Moi-ijaii.— li you could now conveniently let me have 

 duplicates of the moss specimens you sent at the end of March 

 last, it is likely that I could get them identified for you. 



Communications and enquiries on Microscopical matters are 

 cordially invited, and should be addressed to M. I. Cross, 

 Knowledge Office. 326, Hiijh Holborn, W.C. 



NOTES ON COMETS AND METEORS. 



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



Mb. "W. R. Uuuuks and Combtauy Discovekiks.— The dis- 

 coverer of the recent conu't may, perliaps, be regarded as the most 

 successful worlter in this field of astronomy during the last cjuivrter of 

 a century. Between 1882 and 1892 Mr. W. R. Brooks sfiared with 

 Mr. E. K. Barnard the honour of finding the majority of new comets, 

 and if we refer to any general summary of results in this department 

 for the period referred to, the names of these able observers v ill be 

 found to oec\ir with remarkable frequency. But Mr. Barnard relin- 

 quished the scireli some years ago in favour of other important 

 investigat ons; wliilo .Mr. Brooks still devotes himself to it with the 

 same assiduity as ever. In all, lie bus diseoiercd twenty-three cornels, 

 but omitting several objeete which were either inBufticieutly ubaerved, 

 or had been previoutly detected by other obiervel'g, the total number 



of his diecovoricB amounts to nineteen. They have ranged over the 

 last twenty years, so that Mr. Brooks's perseverance in sweeping the 

 heavens has fumislicd us witli an average uf one new comet in a year 

 He found thirteen eometjt with reflecting telescopes of 5 and 9 inches 

 aperture, constructed by liimsclf. and ten comets were first sighted 

 with tho 10 inch equatorial refractor at the Smith Observatory, 

 Ueiieva, New York. Like Messier, Mk'hain, Caroline Hersehcl. Pons, 

 Teiiipel, Winriecke, Swift, Ooggia, Biirrelly, and Harnard, Mr. Brooks 

 has laboured with conspicuous success in a field requiring great 

 patience and discernment, and the valuable as well as numerous 

 results he has obtained have been often acknowledged, and will be 

 duly appreciated by posterity. It is singular how the coui"se of 

 cometary discovery is maintained without serious break from one 

 generation to another. As soon as one observer finds it necessary to 

 relinquish the quest there is another ready to take it up ; thus the 

 firmament is kept under constant surveillani'O, and every year provides 

 additional discoveries or marks the recognition of a known periodical 

 comet. 



TuE Comets of the Ten Years 1802-1901. — Altogether fortv- 

 eight comets were observed, so that the average number was very 

 nearly five per annum. The tiital included thirty-four new comets, 

 while fourteen were observed returns of periodical comets. Compared 

 with the preceding ten years (1882-1891), these discoveries exhibit no 

 increase, for there were fifty-two comets well observed during the 

 earlier decade. 



July and Auofst Meteors. — "With the return of July meteoric 

 studen's realize that the eve of an important epoch has arrived. The 

 first half of the month is usually not nearly so froduetive as the last 

 half, and it is rather imfortunate that in 1902 moonlight will interfere 

 during the fortnight from about July 13th to 27th. With clear 

 weather it will be interesting to look for a number of showers in 

 Pegasus, Cepheus, and Andromeda during the first twelve nights of 

 Jidy, while at the end of the month the Aquarids and Perseids will 

 be pretty certain to furnish a considerable number of meteors. At 

 the latter epoch the moon will rise late, and will have waned sutli- 

 ciently to exercise little influence on the results. Between about 

 July 28th and August l-f-th it will be well to follow the Perseid 

 display as closelv as possible on every suitable night and count the 

 horary numberfef meteors, as well as determine the positions of the 

 radiant The "maximum of the shower will probably occur before 

 sunrise on August 12th, or just possibly on the following morning. 



Fireballs.— Several brilliant objects were observed in May, and 

 the following are some particulars : — 



May 4, 7h. 35^m. — A pear-shaped meteor of considerable size, and 

 giving as much light as a three or four days' old moon, passed from 

 about 10 degrees S. of the zenith to an .altitude of 45 degrees in N.E. 

 Duration about two seconds. Twilight very strong. — E. Rabone, 

 Highgate, N. 



'Ihis object was seen by another observer in the metropolis, who 

 says it was equal to Sirius, and in the N. E. sky, travelling almost due 

 S. to N. It exhibited a planetary disc of a green colour. 



May 16, lib. 52m. — Fireball equal to Jupiter passed from 

 212° •*- 12° to 238° -I- 2J°. Redder than Arcturus. Duration, three 

 seconds. Left a streak. — Rev. W. F. A Ellison, Dublm. 



May 26, lOh. 25m.— Meteor nearly equal to Sii-ius, bencatli 

 p Scorpii, with scarcely any motion, and only 3 degrees above horizon. 

 Position about 236' — 34°. — Bev. S. J. Johnson, Bridport. 



May 27, 12h. 23m. — Splendid meteor starting from hind foot of 

 Ursa Major and falling nearly to horizon at a point directly in line 

 with the direction of ihe fore foot. Of a green colour, followed by a 

 short track of fiery light. Motion extremely slow. The fii-st appear- 

 ance of the meteor was not seen; it died away just before reaching 

 the horizon. Nucleus egg-shaped, with apparently a double tail. 

 Path from about 150° -H 45° to 125" -t- 40", duration 5 seconds.— E. N. 

 CuUuni. Brixton, S.W. — The same fireball was fortunately observed 

 by Prof. A. S. Herschel, at Slough, and he gives the time as 121i. 22m. , 

 and the apparent brightness as one and a half times that of Venus. 

 A comparison of the pair of observations shows that the radiant point 

 was in Sagittarius at 282" — 24°. The meteor moved from a height of 

 63 miles, over a point 7 miles E. of Shrewsbury, to a height of ;'9 

 miles over the sea 20 miles E.N.K. of Douglas, in the Is'.e of Man. 

 Length of observed tliglit 120 miles, and velocity 2 1 miles per secoml. 

 These figures are only approximate. Additional observations kcuIiI 

 be very useful. 



THE FACE OF THE SKY FOR JULY. 



By W. Shackleton, f.r.a.s. 

 The Sun. — On the 1st the sun rises at 3.48 a.m., ami 

 sets at 8.18 p.m. Ou the 31st he rises at 4.23 a.m. aud 

 sets at 7.50 p.m. The earth is at its greatest distance 

 from the buu ou the 4tli at 1 p.m., whmi tho aJ)par<•n^ 

 diameter of the sun is 31' ^0"-6, 



