134 



KNOWLEDGE. 



[June 1, 1900. 



more, so that wc shall obtain a uiuiiber of observations 

 for the greatest and least height of the sun Half the 

 difference between these two must plainly be the 

 obliquity of the ecliptic; and the altitude which is the 

 mean of these two extreme altitudes must be the 

 altitude of the equator, that is to say of the sun when it 

 is at the equinox. The date of the equinox will be 

 determined to the nearest day without any difficulty, 

 for if we set our tube in the meridian, and pointing to 

 the equator — in other words at an altitude equal to the 

 co-latitude of our station — a single day's variation ii> 

 the height of the sun at the time of the equinox will 

 make a change in the position of the sun in the fiell of 

 our pinhole tube of about four-tenths of an inch- -an 

 amount which the very roughest of observers could no*" 

 overlook. 



Such an instrument, simple as it is, would therefo.-e 

 enable the observer to determine the date of the equinox 

 to the nearest day, and consequently the length of the 

 tropical yeai', and also the obliquity of the ecliptic and 

 the co-latitude of the place of observation. The exact- 

 ness with which these could be determined w( uld depend 

 upon the skill and patience of the observer, who could, 

 ere long, if he were sufficiently exact, begin to detect 

 causes of irregularity in his. results, some due to defects 

 in his instrument, and some due to causes apart from 

 that apparent motion of the sun which it was his first 

 object to determine. These we must leave for the 

 present, though their detection and the discovery of 

 their cause would give a keen delight to anyone with 

 a true observer's spirit, especially when he found that 

 a proper allowance for them brought his observations 

 into ever closer and closer accord. 



Utttcrs. 



[The Editors do not hold themselves responsible for the opinions 

 or statements of correspondents.] 



SEAECH FOR AN INTRA-MERCURIAL PLANET. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — "With refei-ence to Prof. E. C. Pickering's pro- 

 posal to search for an intra-mercurial jjlanet during the 

 total phase of the solar eclipse of May 28, I should like 

 to remark that if such a jjlanet exists it is probably 

 exceedingly small. In fact it must be too small to be 

 distinguished when in transit over the sun, or it would 

 certainly have been discovered long ago unless indeed 

 its orbit is much inclined, and it is enabled to pass 

 N. or S. of the sun at its conjunctions, which is highly 

 improbable. The instances of rapidly moving dark 

 spots quoted by Webb may be dismissed as too doubtful 

 to throw any definite light on the subject. The obser- 

 vations are too imperfect to afford data for the satisfac- 

 tory computation of the orbit, though Lescai'bault's re- 

 ported discovei-y of 1859, Mai-ch 26, enabled M. Lu 

 Verrier to derive approximate elements. But Lescar- 

 bault's description is probably the most untrustworthy 

 of all, for the same observer announced to the Academy 

 of Sciences on 1891, January 11th, that he had dis- 

 covered a bright body in Leo, which he could not 

 identify, and had therefore concluded it to be a ne;v 

 star. This " new star " proved to be the planet Saturn : 

 Lescarbault, so easily deluded in this case, was no doubt 

 similarly mistaken in 1859, when a normal sun-spot 

 must have encouraged visions of a mobile planetary 

 body. In this connection it may be added that M. 

 Emmanuel Liais, whose decease has recently been an- 

 nounced, was watching the sun in Brazil at the very 



hour when Lescarbault thought he had detected 

 " Vulcan," and positively averred that no object of the 

 kind was visible. 



At various times I have obtained some thousands uf 

 solai' observations with different instruments, but chiefly 

 with refractors of 4^in. and 3in., and a reflector of 4in. 

 aperture with a view to the detection of an iiitra- 

 mcrcurial planet. The months of observation were usually 

 March — Ajjril, and September — October. On some 

 days the sun was examined at short intervals duriug 

 the whole time that he remained above the horizon, but 

 I never met with any object representing an intra- 

 mercurial planet. Occasionally a suspicious looking 

 spot — pretty round, small, and without penumbra — was 

 noticed, but upon being closely watched it always proved 

 a veritable sun-spot. I believe that spots with certain 

 planetary aspects appear more often than is generally 

 supposed, and perhaps it is no wonder that their charac- 

 ter has been sometimes mistaken by persons who have 

 formed hurried conclusions without applying proper 

 tests. W. F. Denning. 



Bishopstou, Bristol, 

 May 5th, 1900. 



S. U. CYGNI. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — As but little so far as I know has been pub- 

 lished of the movements of Miller & Kempf's Variable, 

 designated by them as S. T. Cygni, and by a late writer 

 in the Agronomical Journal as S. U. Cygni, the following 

 observations though lengthy may be worthy of a portion 

 of your valuable space. 



Maximum due. 

 G.M.T. 



D. H, M. 



Aus-t. -23 17 3!) 

 „' -27 13 55 



„ 31 10 10 



Sept. i 6 25 



8 2 41 



„ 11 22 56 



,, 15 19 11 



., 19 15 27 



,, 23 11 U2 



,, 27 7 58 



Oct. 1 4 Vi 



,, 5 29 



8 20 45 



Maximum due. 

 G.M.T. 



Li. H. M. 



Oct. 16 13 1.5 



24 5 45 



„ 31 22 16 

 Nov. 4 IS 31 



20 3 32 

 23 23 47 



„ 27 20 02 

 Dec. 1 16 17 



5 12 32 



9 8 48 



13 5 03 



17 1 18 



24 17 48 



27 It 04 



These observations were made in the evenings not 

 later than 8 p.m. local time, which is six hours and 

 twelve minutes behind G.M.T. 



Following the elements given by the discoverers I 

 have given the dates upon which maxima were due 

 G.M.T. Their period is 3.844 or 20h. 15m. 21.4, while 

 Luzctte's (Paris) period is 3.846 or 20h. 18m. 14 2, 



