OCTOBKK 1. 1900.] 



KNOWLEDGE. 



239 



Particles of sand and crravel in the alimentary canal of earth- 

 worms that are beini; prepared for sectioninj;. and that may injure 

 the edi;e of the microtome knife, can be removed by feeding the 

 worms on bits of tilter paper before killing; them. 



Mioroscopists will be inteiested to know that certain kinds • f 

 glass appear to be so soluble in water that moisture quickly etches 

 the surface and destroys the transparency. Mr. E. F. Mciudj', of 

 Decca CoUeire. East Beuijal, reports having noticed the dull mutt 

 apfiearance of a cut wineglass and of finger bowls in which water 

 had been allowed to stand; also the spotting of two decanters 

 which had been dried after partial draining. These etVects were all 

 due to water-etching. This explains the rapid deterioration of 

 optic^jl apparatus in the moist climate of India. Proof that the 

 fault is in the kind of glass used is furnished by the object glass 

 of a 3i inch teIescoi>e, the inner surface of the convex lens being 

 badly corroded whilst the adjacent face of the concave lens was 

 quite clear. 



To avoid many of the failures that fall to the lot of the photo 

 miorographer. the details of each experiment that is made should 

 be systematically recorded so that tlie operator may have a gui le 

 on other occasion? when the conditions are similar. For this 

 purpose a book should be kept containing spacings for detiiils 

 regarding the objective, light, distance of light from object and 

 plate, colour of object, plates, screens and time of exposure. 



(ireat care and cle.inliness are necessary in all microscopical 

 work, but particularly in the study of powdered substances. Dust 

 and all other foreign m.atter must be carefully removed from slides 

 and covers. Great caution must be observeil so as not to get 

 different powders mixed. The s;ime slide should never be used 

 for different powders unless special care has been observed in clean- 

 ing them. If several slides are being prepared for examination be 

 sure to label them, otherwise confusion is sure to follow. 



Of all the media employed for the mounting and preservation of 

 objects Canada balsam is the most generally useful, and it is 

 probable that more objects are mounted in this material than m 

 all others put togetlier. It is perfect as a preservative, and its 

 action in rendering many objects transparent is often of great value. 

 Much of the Canada balsam that is sold is made of cheap resins 

 dissolved in impure turpentine, and this explains many of the 

 diflSculties and failures that fall to the lot of the microscojiist. To 

 be good Canada balsam shoidd be of thick consistence, nearly 

 coloTirless, and thoroughly transparent. 



In mounting; objects in balsam the great difficulty to be en- 

 countered is the presence of air bubbles. Judicious management, 

 however, enables one to avoid them. In the first place all Ijubbles 

 should be removed from the bals.nm on the slide. This is more 

 easily done before immersing the object in the balsam than after- 

 wards. Xext see that the air is expelled from the object ; and 

 lastly, that no air enters with the cover. To do this the cover 

 should be made hot, and then slowly lowered on tlie balsam from 

 one side. 



Dr. E. J. Spitta finds that, when taking photographs of living 

 bacteria such as the clumping of the typhoid germs in Widal's 

 method of diagnosis, it is best to take advantage of diffraction 

 effects and to close the iris to what would otherwise be ((msidered 

 an undue amount. By this means a faint ".standing out" effect is 

 produced which enables the bacteria to show sufficiently for the 

 purpose, provided the exposure be short enough to prevent choking 

 effects, and yet long enough to give a sufficiently dense background. 

 He finds that ten seconds is sufficient with a subdued light, and 

 using a one-sixth apochromatic objective. A vertical apparatus 

 must be used. 



To mount the antenn;e of flies, wasps, and bees, it is necessary 

 to soak the objects in chlorate of potash, with a few drops of 

 hydrochloric acid, until they are colourless, and then mount 

 in Canada balsam and benzole. The points requiring attention are 

 these : soaking just the right length of time in the' i)otash, for if 

 the object remains too long in the liquid it will be destroyed ; and 

 manipulating it when mounting so as not to destroy the character- 

 istic features. 



[All communicationn in reference, (o this Column xhonld le 

 addressed to ifr. J. U. Cooke at tlie Office of Knowledge.] 



THE FACE OF THE SKY FOR OCTOBER. 



By A. Fowler, f.r.a.s. 



The Sun. — On the 1st the sun rises at 6.2 and sets at 

 5.38; on the 31st lie rises at 6.53 and sets at 4.35. 



The Moon. — The moon will enter first quarter on the 

 1st at 9.11 P.M. ; will be full on the 8that 1.18 p.ii ; will 

 enter last quarter on the 1.5th at 9.51 a.m.; will be new 

 on the 23rd at 1.27 p.m.; and enter first quarter again 



oil llu- :Ust at 8.18 A.M. The following are among the 

 principal occultations visible during the month: — 



S 



S o 

 S>5 



a 





a 



a 

 Is 



1^ 



l1ct. 1 



H. A. c. (avi 



li. A. C, (.710 

 K Pisciuni 

 uj ^ Tanri 

 V Geuiinonuu 

 5 Sagittnvii 



6-0 

 liO 

 5-0 



■10 

 ID 



8..')2 P.M. 



lO.S P.M. 



l.:^5 A.M. 



8.-tr P.M. 

 :i.o .».M. 

 8.27 P.M. 



S-i 

 :U 

 :is 



■to 



9.41 P.M. 

 10..5S P.M. 



2.ai A.M. 



!l.'_^^ P.M. 

 ;i.i;! .\.M. 



8.11) P.M. 



dTll. 



7 2.'-. 



8 2rt 



y.i n 



17 25 

 20 7 

 6 8 



TiiK Pl.^nets. — Mercury is an evening star throughout 

 tlie mouth, at greatest eastern elongation of ncai'ly 24° 

 on the 30th, but is too far south to be easily observed 

 ill our latitudes. 



Venus remains a morning star, rising on tlio l.=;t about 

 1.15 A.M., and on the 31st about 2.50 a.m. The planet 

 is in Leo until the 28tli, and will bo less than a degree 

 south of Regulus on the 7th. At the middle of the 

 month the diameter of the planet will be 18". 4, a little 

 more than si.x-tentlis of the disc being then iliuminatod. 



Mars rises a little before midnight throughout the 

 month, and is gradually becoming more favourably 

 placed for observation. The planet has an easterly 

 motion, passing from Cancer into Leo about the 25th. 

 On the 15th, the apparent diameter of the planet is 

 5". 8, and the illuminated part 0.902; the distance of 

 the jjlanet from the earth at this time is nearly 140 

 millions of miles. 



Jupiter is still an evening star, in Scorpio, but too 

 close to the sun for observation, except under very 

 favourable circumstances. At the beginning of the 

 month the planet sets before eight o'clock, and at the 

 end of the month soon after six. 



Saturn remains an evening star, in Sagittarius, setting 

 soon after 9 p.m. on the 1st, and about half-past seven 

 on the 31st. 



Uranus is an evening star, but so near the sun, and 

 so low, that it may be considered not observable. 



Neptune rises soon after 9 p.m. on the 1st, and soon 

 after 7 p.m. on the 31st. He is stationary on the 2nd, 

 and afterwards describes aj short westerly path in 

 Taurus, almost midway between 132 Tauri .^nd Eta 

 Geminorum. 



The Stars. — About 9 p.m. at the middle of the month, 

 Auriga and Perseus will be in the north-east; Taurus 

 low down in the east; Aries, Pisces, and Cetus in the 

 south-east; Andromeda and Cassiopeia high up and a 

 little south of east ; Pegasus and Aquarius in the 

 south; Cygnus high up to the south-west; Aquila a 

 little lower in the south-west; Lyra and Hercules to- 

 wards the west; Corona towards the north-west; and 

 Ursa Major in the north. 



Minima of Algol will occur on the 9th at 10 40 p.m., 

 and on the 12th at 7.29 p.m. 



(JE!)css CToIttmn. 



By C. D. LococK, b.a. 



♦ 



Communications for this column should be addressed 

 to C. D. LococK, Netherfield, Camberley, and be posted 

 by the 10th of each month. 



Solutions of September Problems. 

 No. 1. 

 (N. M. Gibbins.) 

 1. Kt to Kt3, and mates next move. 



