lis 



KNOWLEDGE. 



[May, 1903. 



NOTES AND QUERIES. 



W. N. T. — The merits of all the microscopes you name are so 

 close that it is impossible to recommend one in preference to 

 another. So much depends on your future intentions, and if you 

 propose to do progressive work preference should be given to 

 an instrument which can have extra fittings added to it 

 from time to time to make it quite complete. For the work 

 you name, you would find a No. 2, or '• B," ocular, in conjunc- 

 tion with 1 inch and 5 inch objectives, the most serviceable. It 

 is unlikely that you would require both the r| inch and ^ inch ; 

 and I certainly should not advise the use of a deep-power 

 eyepiece for the comparatively low-power objectives for con- 

 tinual work. Better results are always secured with eyepieces 

 of low power. 



W. Bor/ers. — (1) Treatment of Fossil Deposits for Diatoms. — 

 Break deposit up into small pieces and boil in a strong solution 

 of soda bi-carbonate, pour ofl" from time to time the disintegrated 

 material into a beaker, and continue the boiling until all the 

 deposit has broken up. The soda solution must then be washed 

 away and the diatoms boiled for about 15 minutes in nitric acid, 

 and, when clean enough, wash away the acid with repeated 

 changes of water, then boil up the diatoms in distilled water. 

 (2) Treatment of Sponges. — If horny, boil in liq. potassa;, then 

 wash spicules with water to remove all trace of potash and 

 mount them in glycerine jelly or Canada balsam. Siliceous 

 sponges must be boiled in nitric acid, then washed well with 

 water and mounted in glycerine jelly or Canada balsam. For 

 types in which siliceous spicules are embedded in horny matrix, 

 boil in liq. potassas for a few minutes to disintegrate the 

 spicules, then boil in nitric acid to clean spicules, wash away 

 acid with repeated changes of water and mount in glycerine 

 jelly or Canada balsam. ('A) To male Camphor Water. — Add 

 some pieces of camphor to distilled water and let it stand for 

 24 hours, filter, and then you will have a 3 per cent, solution ; 

 water will not take up more. Another way : Dissolve some 

 camphor in rectified spirit, add a few drops of distilled water, 

 shake well for a minute, filter, and keep in a stoppered bottle. 

 (4) I consider a 2 inch objective better for small seeds. 



C. Zimmeriaann. — (1) The parasite on the portion of pear tree 

 you send is the Pearl Oyster Scale (Aspidiotus ostrenformis !. 

 (2) The only fixing medium I know of for celloidin sections is 

 Majer's albumen, but I do not think any is required; the celloidin 

 need not be removed. The tissue should be stained in bulk, 

 embedded in celloidin, cut sections, place in absulute alcohol 

 for about three minutes, clear in oil of origanum, and mount 

 in Canada balsam. The celloidin will be invisible. (3) There 

 is only one solvent for celloidin, viz., eiiual parts of absolute 

 alcohol and ether. 



Communications and enquiries on Microscopical matters are 

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

 Knov?ledge Office. 326, Bigh Holhorn, W.C. 



NOTES ON COMETS AND METEORS. 



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



GiACOBixi's CoMKT (1902 i)\— This small, distant comet is still 

 visible in the evenings, and will be situated abnut 2'^ E.N.E. of 

 a Getninorum at the opening of May, and moving slowly eastwards. 

 Recent obsorvations have fully confirmed tlie exceptionally great 

 perihelion distance (258 millions of miles) di'rived from earlier com- 

 putations. This distance is 118 millions of miles outside the mean 

 position of the orbit of Mars and in the region of the minor planets. 

 On May 1 the comet will be about 280 millions of miles from the 

 earth. 



Peeiobicat, Comets.— Several short-period comets, belonging to 

 the Jovian family, are due to return to perihelion tliis year, but the 

 conditions will be unfavourable in most eases, so that the objects will 

 probably escape observation. Giacobini's comet of 1896 (V.), formerly 

 supposed to have a period of 9 years, appears to revolve in only 6 647 

 years aicording to new elements computed by Ebell (Ast. Nach. 3848). 

 It will return during tliepi'esent spring, but only as a very faint object. 

 Perrine's comet of 18;'6 (YIl ) should pass through perihelion on 

 jipril 26, and Risteupart gives elements corrected for perturbation by 

 Jupiter in Ast. Nach. 38il. But the prospect of seeing the object is 

 extremely small, for when at its briglitest in May it will hare only 

 half the light which it displayed when last seen in 1897 at Northfield, 

 Minn., on which occasion the aspect of the comet was described as 

 " most exceedingly faint " as viewed in a 16-ineh refractor. Spitaler'a 



comet, 1890 (VII.), is due in the summer, but it is a feeble object, 

 and will not be sufficiently well placed to be re-observed. Faye's well- 

 known comet ouglit to be fairly well seen in the autumn, and Brooks's 

 comet (1889 (V,)— 1896 (VI.)) will rearli perdielion next December, 

 but will be nearest to the earth at the mitldle of August. Its periodic 

 time is 2592 days (7'1 years), and Seagrave has computed a search 

 ephemeris from which we hope to give extracts in later months. 



Sounds accompantixo Metroks and Meteorites. -Casual 

 observers sometimes report that they distinctly beard, simultaneously 

 with the (light of a meteor, a hissing, rushing or whirring sound. 

 Many instances of this might be quoted from descriptions of meteoric 

 apparitions in recent years. But judging from the circumstances and 

 from the nature of the evidence there seems little reason to doubt 

 that in all such cases the contemporary sounds were either imaginary 

 or produced from sources altogether different to those assigned. 

 Sound is a slow traveller, and even admittingthat a meteor penetrates 

 the air to within 25 mdes of an observer, the noise of its disruption or 

 concussion could not reach him until 2 minutes afterwards imless 

 there is some law of acoustics not yet understood. 



In the case of a meteorite close to the earth's cruet, and in the act 

 of subsiding upon it, the conditions are essentially dissimilar, for its 

 detonations may startle an observer before he sees the falling body 

 strike the earth. This arises from the remarkable slowness of motion 

 with which the object is travelling. Meteorites usually penetrate the 

 soil to the depth of only a foot or so, from whence it is evident that 

 their velocity can scarcely exceed a few hundred feet per second. 

 The meteorite which fell at Wold Cottage, Yorks, on 1795, December 

 13, was dug out of a hole 18 inches deep. The meteorites of 1876, 

 April 20, and 1902, September 13, embedded themselves to the same 

 depth as that of 1795, while that of 1881, March 14, was discovered 

 11 inches below the surface. 



The question of the precedence of souud in attracting attention to 

 these events formed the subject of an interesting discussion at a recent 

 meeting of the British Astronomical Assuciation, but the matter 

 seemed difficult to explain, as the speakers appeared to regard 

 parabolic or planetary speed as one of the necessary features of falling 

 meteorites. But atmospheric resistance, and, in lesser degree, terres- 

 trial attraction, must exercise a greatobstructive influence upon objects 

 of this class, robbing them of liheir initial speed and direction, and 

 ultimately causing them to descend upon the earth with a velocity 

 comparable with that of terrestrial bodies. When the meteorite of 

 1881, March 14, reached the earth's surface its velocity was only 412 

 feet per second (1 mile in 13 seconds) according to some experiments 

 specially carried out by Prof. Herechel. The object would have 

 acquired this rate by falling freely through \ mile, while if vertically 

 descending through 40 miles it would have reached the ground with 

 a velocity nine times as great as that observed. *' Sebiaparelli has 

 shown that if the law of resistance for planetary motions is simdar 

 to that derived from experiments with artillery, then a ball of 8 inches 

 diameter and 32 i lbs. weight entering the atmosphere with a velocity 

 of 44t miles per second will on arriving at a point where the 

 barometric pressure is still only yi^, of that at the earth's sur''ace, 

 have its velocity already reduced to3^milesa second." Such meteors, 

 therefore, as are sufficiently large and compact to be practically 

 stopped in their courses before disruption and dissolution, will become 

 cooler, and descend leisurely to the earth, sometimes travelling with 

 a velocity less than that of sound, so that the intimation of their 

 downfall is conveyed to the ear quicker than to the eye of a spectator 

 who may happen to be near. 



THE FACE OF THE SKY FOR MAY. 



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



The Sun. — On the 1st the sun rises at 4.37 and sets at 

 7.19 ; on the 31st he rises at 3.53 and sets at 8.2. 



The minimum of svmspot activity seems now to be left 

 well behind, and spots of considerable size have Ijeen 

 recently recorded. At the time of writing there is a fairly 

 large spot near the central meridian. 



The Moon : — 



The moon is in perigee on the 1st and 28th, and in 

 apogee on the 16th. 



