March i, 1894] 



NATURE 



41. 



Thus it appears that N. clavipes is not altogether unworthy of 

 comparison with the great Madagascar species in regard to its 

 web. It is one of the very commonest spiders of Jamaica, as 1 

 have myself observed, and has a wide distribution in the neo- 

 tropical region. T. D. A. COCKERELL. 



Las Cruces, New Mexico, U.S.A., February 8. 



The Cloudy Condensation of Steam. 



With reference to Prof. Barus's letter (p. 363), I have never 

 suggested that condensation nuclei in smoke, &c. would 

 • ' remain distinct indefinitely, " but that, if there were no chemical 

 action, they would hardly disappear in the course of a few 

 seconds. . . • . » 



There is no mention in my lecture of " dissociated particles, 

 or of the dissociation of platinum at red heat. What I said was 

 that electrical discharges and incandescent substances probably 

 caused dissociation of oxygen and nitrogen in the surrounding 

 air {ante, p. 214). Shelford Bidwell. 



February 22. 



Astronomy in Poetry. 

 With reference to the note in the Astronomical Column of 

 Nature, No. 1226 (p. 372), it is worth remark that the nebular 

 theory of the universe is briefly and accurately set forth by 

 Tennyson thus — 



" This world was once a fluid haze of light, 

 Till toward the centre set the starry tides 

 And eddied into suns, that whirling cast 

 The Planets." \The Princess.l 



A little knowledge of astronomy would have led Coleridge's 

 Ancient Mariner to know that he could never have seen 



" The horned moon, with one bright star within the nether tip." 



Tennyson is always accurate in his descriptions of natural 

 phenomena. Edward Geoghegan. 



Bardsea, February 19. 



A Plausible Paradox in Chances. 



With reference to the paradox in chances mentioned by Mr. 

 Francis Gallon in Nature of February 15 last, I think 

 the following remarks will show very simply where the fallacy 

 lies. 



If I assert that at least two out of three coins must turn up 

 alike, I am saying what is evidently true ; but if I go on to say 

 that it is an even chance whether a third coin is head or tail, I 

 am assuming that only two coins have been tossed, and that the 

 fate of the third is still uncertain ; but this is directly counter to 

 my first assertion, which requires the tossing of three coins. 



If this method of reasoning is to be used at all, I must say 

 first that the chance of two coins turning up alike on being 

 tossed is h, and then that the chance of a third coin being the 

 same as the other two is also i, and that therefore the required 

 chance of all three being alike is i x 2 o"" i- 



Lewis R. Shorter. 



THE PLANET VENUS. 



Tj^ROM time immemorial the planet Venus has 

 -*- attracted the attention of mankind. Before the days 

 when the " optic tube " began to be turned towards her 

 disc, Venus, we might say, was still in myth, and she was 

 hailed as Hesperus and Phosphorus, according as she 

 was an evening or a morning star, the fact that the 

 same object was in question being then unknown. 



Shining as she does at times with a brilliancy surpass- 

 ing any other body except the moon, it is only natural 

 that she should have been so often sung about by poets 

 in all lands, liking her unto 



" the fair star 

 That gems the glittering coronet of morn." 



And she is highly honoured by Homer, in that she is the 

 only planet to which he refers : 



"EffTrepos OS kUWkttos iv ohpavcf "ararai daTr]r]p. 

 Hesperus quae pulcherrima in coelo posita est Stella. 



NO. I 270, VOL. 49] 



To Galileo belongs the honour of first having viewed 

 the planet through a telescope, but it is curious to re- 

 mark the lapse of time that he allowed to pass before he 

 made his first observation. The discovery that Venus 

 exhibited phases did not take place until the end of 

 September 1610, though Galileo first observed the satel- 

 lites of Jupiter on January 7 of that year. 



That Galileo should veil this important discovery of 

 the phases of Venus under a Latin anagram,^ does seem 

 at first rather strange, but when one considers the vast 

 importance of the discovery in that it supplied a simple 

 proof of the planet's revolution round the sun, one can 

 understand that he would first desire to be quite certain 

 of his facts before giving the key to the anagram. 



An historical fact of interest with reference to Father 

 Castelli maybe mentioned here. In Venturi's collection 

 there is a letter from Father Castelli to the celebrated 

 Florentian astronomer, dated November 5, 1610, in which 

 he asks Galileo whether Venus and Mars show phases. 

 Galileo evidently did not wish to give a direct answer, so 

 evaded the question by saying that, although he was en- 

 gaged in various investigations, he was better in bed 

 than out in the open air in consequence of great in- 

 firmity. It was not until December 30, 1610, that he 

 informed Castelli of his recognition of the cusps. 



Fig. I. — February 20, 1070 (Trouvelot). 



With an ever-increasing number of telescopes at the dis- 

 posal of astronomers, it is not astonishing that facts con- 

 cerning surface markings, form, period of rotation, &c. 

 should be rapidly forthcoming, and the sum total of what 

 we now know about the planet has been gained at the 

 expense of much labour and patience at the eye-piece 

 end of the telescope. 



During the past three months Venus has been a 

 striking object in the south-western and western region 

 of the sky, being in a position more than usually favour- 

 able for observation. Towards the end of November 

 last her great southern declination began to decrease, 

 while the planet became brighter and brighter, passing 

 her greatest elongation east on December 6. On 

 January 11 she attained her maximum brilliancy, the 

 crescent form gradually increasing until on February 15, 

 that is, at inferior conjunction, it was totally invisible. 

 Gradually the crescent will become visible again, but in 

 the inverse order, and we shall have another maximum on 

 March 22, superior conjunction occurring on November 

 30. Thus we know that Venus is now lost in the sun's 

 rays, and is, in consequence, invisible to us as an evening 

 star for some time to come. The accompanying iliustra- 

 tion (Fig. i) gives a drawing of the planet as recorded by 



1 " Hsec immatura a me jam frustra leguntur,"or with the letters properly 

 arianged — "Cynthiae figuras aemulatu Mater Amorum." 



