September 1, 1890.] 



KNOWLEDGE 



219 



has attained a length of about twice its own diameter, and 

 then darting forth with lightning rapidity. At this instant 

 he said he had in many instances " heard a distinct crack." 

 The writer believes this to have been a delusion. It often 

 occurs in watching the jaws of a large Brachion rotifer, 

 and similar apparatus. A movement which if perfonned 

 by a mechanism large enough to affect our hearing would 

 make a crack or snap-like noise, is readily imagined to do 

 so when the eye watches a magnified image under the 

 microscope. There are many much simpler poison-threads 



Fig. 2. 

 Tkichodina pediculus. 



Figs. 3 and 4. 

 Kerona polypoktjm. 



than that in the figure. Those in the polyp are far less 

 elaborate but instantly eft'ectual. 



Fig. 2 represents Trirhodinn lu'iHitdnx seen from above 

 in full face. Besides delicate cilia, it has a wreath of 

 horny dentich's, or little teeth. A side \-iew, when it runs 

 about, shows it as a squat cylinder. Its skin is very 

 flexible, and it can assume various shapes, disc-like, conical, 

 hour-glass, &c. 



Figs. 8 and 4, Kcnnut ji(di/ii<in(iii, ventral and dorsal 

 aspects. It belongs to the Hi/jidtn'rliH, which have x 200 

 thin locomotive cilia on the ventral surface only. It has 

 not, like the Ti-irhmUna, the power of changing its shape. 

 It is a greedy animal, eating both animals and vegetables, 

 but it abstains from feeding upon its host the polyp. 



THE FACE OF THE SKY FOR SEPTEMBER. 



By Hekbert Sadler, F.E.A.S. 



THE abnormal paucity of sun-spots still continues. 

 Conveniently observable minima of Algol occur at 

 6h. 12m. P.M. on the 1st; llh. -Im. p.m. on the 

 18th ; and 7h. 52m. p.m. on the 21st. Mercury 

 is an evening star during the first half of the 

 month ; but is very badly situated for observation, owing 

 to his proximity to the sun. As the interval between the 

 setting of the sun and planet does not exceed half-an- 

 hour throughout the month, any details would be useless. 

 He is at his greatest eastern elongation (27°) on the 3rd, 

 and is in inferior conjunction on the 29th. 



Venus is an evening star, but is not well situated for 

 observation owing to her southern declination. She sets 

 on the 1st at 7li. 59m. p.m., Ih. 13m. after the sim, with 

 a southern declination of IQ\°, and an apparent diameter 

 of 19J". On the 30th she sets at 6h. 44m. p.m., Ih. 5in. 

 after the sun, with a southern declination of 22' 20', 

 and an apparent diameter of 20.',". About the middle of 

 September she appears as a moon about her last quarter ; 

 and is at her greatest eastern elongation (46|°) on the 24th. 

 During the mouth she passes from Virgo into Libra, but 

 without approaching any conspicuous naked-eye star. 

 Mars is an evening star, and our remarks in last month's 

 " Face of the Sky," as to his telescopic aspect, will, un- 

 fortunately for the amateur, rather gain than lose in 

 strength. The planet sets on the 1st at 9h. 5m. p.m., with 



a southern declination of 25f °, and an apparent diameter 

 of IM". On the 30th he sets at 9h. 17m. p.m., with a 

 southern declination of 25° 55', and an apparent diameter 

 of '.)\" . At the latter date his brightness is only about one 

 quarter of what it was at opposition, and about ^rro of the 

 disc will be hidden from new. Mars is in quadrature 

 with the sun on the 21st, and passes during the month 

 from Ophiuchus into Sagittarius, but without approaching 

 any bright star very closely. 



Jupiter is an evening star, rising on the 1st at 5h. 26m. 

 p.m., with a southern declination of 20° 10', and an ap- 

 parent equatorial diameter of 46-i-". On the 30th he rises 

 at 3h. 28m. p.m., with a southern declination of 20° 26', 

 and an apparent equatorial diameter of 43'0". The fol- 

 lowing phenomena of the satellites occur while the planet 

 is more than 8° above, and the sun 8° below, the horizon. 

 A transit ingress of the first satellite at Oh. 29m. a.m. on the 

 2nd, an occultation disappearance of the same satellite at 

 9h. 49m. p.m., and a transit ingress of the third satellite 

 at llh. 52m. p.m. A transit ingress of the shadow of the 

 first satellite at 7h. 46m. p.m. on the 3rd ; a transit egress 

 of the satellite itself at 9h. l6m. p.m., and a transit egress 

 of its shadow- at lOh. 6m. p.m. An occultation disap- 

 pearance of the second satellite at 9h. lOm. p.m. on the 

 5th. An eclipse reappearance of the third satellite at 

 8h. 49m. 49s. p.m. on the 6th. A transit egi-ess of the 

 shadow of the second satellite at 8h. 58m. p.m. on the 7th. 

 An occultation disappearance of the first satellite at 

 llh. 36m. P.M. on the 9th. A transit ingress of the first 

 satellite at 8h. 44m. p.m. on the 10th, a transit ingress of 

 its shadow at 9h. 41m. p.m. ; a transit egress of the satellite 

 at llh. 4m. p.m., and of its shadow one minute after mid- 

 night. An eclipse reappearance of the first satellite at 

 9h. 19m. 40s. p.m. on the 11th. ka occultation disap- 

 pearance of the second satellite at llh. 31m. p.m. on the 

 12th. An occultation reappearance of the third satel- 

 lite"at 8h. 51m. p.m. on the 13tli, and an eclipse disap- 

 pearance of the same satellite at 9h. 18m. 41s. p.m. A 

 transit ingress of the shadow .of the second satelhte at 

 8h. 40m. P.M. on the 14th ; a transit egress of the satel- 

 lite itself at 9h. 32m. p.m., and of its shadow at llh. 35m. 

 P.M. A transit ingress of the shadow of the fourth satellite 

 at 7h. 25m. p.m. on the 16th (the shadow crosses the 

 central meridian at 9h. 50m. p..m.). A transit ingress of 

 the first satellite at lOh. 32m. p.m. on the 17th. An occul- 

 tation disappearance of the first satellite at 7h. 52m. p.m. 

 on the 18th, and an eelii^se reappearance of the first 

 satellite at llh. 14m. 57s. pm. A transit egress of the 

 first satellite at 7h. 20m. p.m. on the 19th, and of its 

 shadow at 8h. 25m p.m. An occultation disappearance of 

 the third satellite at 8li. 47in. p.m. on the 20th. A transit 

 ingress of the second satellite at 9h. 2m. p.m. on the 21st, 

 and of its shadow at llh. 17m. p.m. An eclipse reappear- 

 ance of the second satellite at 8h. 18m. lis. p.m. on the 

 23rd. An egress of the shadow of the third sateUite at 

 6h. 53m. p.Ji. on the 24th, and an occultation reappear- 

 ance of the fourth satellite at 9h. 32iu. p.m. An occulta- 

 tion disappearance of the first satellite at 9h. 42m. p.m. on 

 the 25th. A transit ingress of the first satellite at 6h. 

 50m. p.m. on the 26th, a transit ingress of its shadow 

 at 8h. Om. p.m. ; a transit egress of the satellite itself at 

 9h. lOm. P.M., and of its shadow at lOh. 21m. p.>t. .Aa 

 eclipse reappearance of the first satellite at 7h. 39in. 4s. 

 on the 27th. Jupiter describes a very short retrograde 

 path in Caprieornus during the month, but does not 

 approach anv naked-eye star. He is stationary on the 

 28th. 



Saturn and Uranus are practically invisible. Neptune 

 is an evening star, rising on the 1st at 9h. 48m. p.m., 



