NOTES 



A. C 



ASTRONOMY. 



D. CkoMMEi.iN. H.A.. D.Sc. l-'.R.A.S. 



STFLLAR PARALLAXES.— r/;f Astruphysiail Joiini.il 

 fur July contains an interesting paper by Frank SclilesniijLT 

 on llie pliotographic determination of stellar parallaxes with 

 the Yerkes' refractor. There has been a great advance in 

 accnrac\- in recent years, and the probable error of deter- 

 mination is of the order 0"-02. One general 

 resnlt derived is the great distance of the 

 helium stars; four fourth-magnitude stars of this 

 type are of sensibly the same distance as the 

 ninth-magnitude comparison stars. The following 

 table gives the parallaxes deduced whore thev 

 exceed 0"- 1 : — 



Star ,!''"''• P:irall;iv. 



Struve 2398 2" -28 "-2') 



Groombr 34 2"-85 "-27 



BD-f56'-2783 0"-92 ... ... "-2.^ 



\VB V 592 Z"-25 "-19 



Lai 25372 2"-ii ... ... "-15 



Lai 46650 l"-40 "-15 



LallFn457,145H l"-69 "-15 



WB XVII 322 l"-36 "■\4 



At Cassiop 3"- 75 "-11 



b Aquilae 0"-96 "-10 



th 



On October 4th it is 10 East of Cor Cuioli (a Canuni \'en.l. 



On October 12th it is near /i Comae. On this day it is in 

 conjunction with the Smi, 36° North of it: after this it may 

 be best seen in the morning, though \ isible in the evening for 

 a few nights longer. 



ENCKE'S COMET. — M.Gonnessiat gives in Astr. Nachr. 

 4518, particulars of his observations of. Encke's Comet on 

 July 31st and August 1st. ItsVfinding was the resnlt of 



parallax 



nnu'li Inighter 



light was rc- 



kcep its image 



Wlirie 

 than the comparison 

 duced by a rotating 



small and measurable. This plan worked very 

 successfully. He estimates that tlu' niunlur 

 of parallaxes that can be determined per annum 

 this telescope is equal to the nnmber of 

 plates being taken 

 jf each star during 

 the vear. 



uitli 



Inie nights, about thirteen 



on each night, and thirteen 



COMETS.— The 

 19116 (Kiessi and 



following revised elements of Comets 

 191 U- (Brooks) are by Dr. Kobold :— 



( ..,iu\. Kicss. 



Tin Berlin M.T. .. 191 1, June 30- 3093 1911. Oct. 27- 762 



Omega 110 ii' 50" 



Node 157 26' 21" 



Inclination... ... 1 18 27' 25" 



Equinox 1911-0 



Log q. ... ... 9-83565 ... 



Both comets were evidently difficult objects to observe 

 accurately, as there are large discordances which, in the case 

 of Kiess, suggest that the orbit differs sensibly from a paraliola. 

 This comet is now too far South to be seen in l-^ngland. and 

 has also sunk to the tenth magnitude, but Brooks' will be a 

 conspicuous naked-eye object in the evening sky early in 

 October. It was half a magnitude fainter than the Andromeda 

 nebula on August 29th, and its intrinsic brightness is likely to 

 increase considerably as it approaches the Sun. so thai it may 

 reach the second magnitude. 



ICphemeris for 1 1 p.m. : — 



K.A. 



N.Dec. 



K.A. 



N.Dec. 



Oct. 



Oct. 



On September 30th it is 2 Soi 

 continuation of the tail ol the Great Bear. 



FiGL'Ki; 1. Encke's Comet. 



patient search, and it could only be seen on these two 

 mornings, and then only for a few minutes between its rising 

 and the dawn. On August 1st it was thought to be of 

 magnitude seven-and-a-half. 



The predicted date of perihelion was 1911, .\ugust 19- 0656. 

 Berlin M.T. The observation of K.A. indicates that this 

 should be increased by O"- 178, that of declination by 0''- 128. 

 Giving the R.A. greater weight, we may take August 19-23 as 

 a close approximation to the actual date. The error of the 

 predicted value is larger than Professor Backlund expected : 

 he notes in Astr. Nticlii:. 4518, that it is not due either to 

 errors in the computed perturbations or to a wrong mass of 

 Mercury. Presumably, it arises from an alteration in its rate 

 of acceleration, which has taken place several times before. 

 There is a simple way of making pretty accurate forecasts of 

 the dates of perihelion of this comet bv taking advantage of 

 the fact that eighteen revolutions of the comet are nearly 

 equal to five of Jupiter, and consequently the perturbations 

 nearly repeat themselves after this interval. Table A gives 

 all the observed perihelion and the interval in days between 

 each perihelion and the one eighteen revolutions later. 



These are plotted in the diagram above (Figure 1) and it 

 will be seen that they lie on a sinuous curve, from which the 

 next return (that of 1914) has been predicted. It will probably 

 not be much more than a day in error. The return of 1911 

 was predicted from the curve 0-8 days too late. The comet is 

 most conspicuous at winter returns. Those of 1786, 1795. 



401 



