226 



NATURE 



[January 5, 1893 



translated into intelligible form the various terms of one of the 

 less formidable formulae of Mr. Heaviside's memoir, I was 

 surprized to find two old and very unpretending friends 

 masquerading in one person like a pantomime Blunderbore. 

 In one of his Avatars the monster contains, besides the enclos- 

 ing brackets, no fewer than 24 letters, 12 suffixes, 3 points, and 

 5 signs ! When he next appears he has still the brackets to 

 hold him together, but although he has now only 18 letters, he 

 makes up his full tale of 44 (or 46) symbols ; for he has 9 

 suffixes, 3 indices, 3 points, 5 signs, and 3 pairs of parentheses .' 

 I used to know him as compounded of 14 separate marks only, 

 viz.: — V-V'r+ 2SvV]S(r'ri: — but, unless I had required to 

 dissect him, I should never have put him in anything resembling 

 his new guise. 



Dr. Knott's paper is, throughout, interesting and instruc- 

 tive : — it is a complete exposure of the i retensions and defects 

 of the (so-called) Vector Systems. " Wer diesen Schleler hebt 

 soil Wahrheit schauen ! " I find it difficult to decide whether 

 the impression its revelations have left on me is that of mere 

 amused disappointment, or of mingled astonishment and pity. 



P. G. Tait. 



Edinburgh, 24/12/92. 



Measurement of Distances of Binary Stars. 



With reference to Mr. C. E. Stromeyer's letter on the above 

 subject, which appeared on p. 199, it maybe of interest to point 

 out that his plan of determining the distance of a binary star is 

 by no means a new one. 



The method was, I think, first suggested by Mr. Fox Talbot 

 at the Edinburgh meeting of the British Association in 1871 ; 

 but the mere idea was sufficiently obvious as soon as the pos- 

 sibility of determining velocities by the spectroscope had been 

 demonstrated by Dr. Huggins. 



The first discussion of the geometrical conditions of the 

 problem was given by Prof. C. Niven in the Monthly Notices, 

 vol. xxxiv. No. 7, where he exhibits the relation connecting 

 the parallax, the relative velocity, and the elements of the orbit 

 of a double star, and computes the value of the product (irV) i 

 of the parallax and velocity for a small number of binary 

 systems. 



In a paper published in the Proceedings of the Royal Irish 

 Academy for May, 1886, I examined the same question from a 

 slightly different point of view, being at the time unaware of 

 Prof. Niven's paper, and was led to similar results. An epitome 

 of this paper was published in your Astronomical Column, 

 vol. xxxiv. p. 206. From the results obtained it appeared 

 that, all things considered, 7-Coronse Australis and o-Centauri 

 were the most likely binaries to yield to this method of eliciting 

 the secret of their parallax, while o-Geminorum, one of the stars 

 selected by Mr. Stromeyer, was shown to be most unfavourable 

 on account of the situation of its orbit. 



In the Monthly Notices for March, 1890, I again drew atten- 

 tion to the subject in view of the accuracy of the results ob- 

 tained by the photographic method in the hands of Prof. 

 Pickering and Prof, Vogel. In this paper I gave an extended 

 list of binaries with the usual geometrical and dynamical 

 elements, and in addition the two elements A and B on which 

 the relative velocity depends. I also gave the greatest value 

 which irV can attain in each case and the velocity to be expected 

 in the case of those stars whose parallaxes had been de- 

 termined. 



Again in Mr. J. E. Gore's valuable catalogue of Binary Star 

 Orbits, published in the Proceedings of the Royal Irish Academy 

 for June, 1890, columns 18 and 19 are devoted to the constants 

 A and B computed from my formulae (which I may say ought 

 more properly to be called Prof. Niven's formulas on account of 

 the priority of his paper) for eighty-one different orbits. 



The subject has also been discussed by Miss Gierke in " The 

 System of the Stars," pp. 199-201, where references to most of 

 the original publications will be found. 



I may perhaps add that the inverse problem of determining 

 the elements of the orbit from spectroscopic observations alone 

 has also been investigated by me in the Monthly Notices, vol. li. 

 No. 5, where I have deduced the principal elements of the orbit 

 of ^ Aurigae, a spectroscopic double which no telescope can 

 divide. 



I have been disappointed that astronomers engaged on spec- 

 troscopic determinations of stellar velocities have not devoted 

 anore attention to observations of already known binaries, which 



appear to me to offer a promising field of work, and have often 

 regretted that at this observatory we have not the means of 

 undertaking the investigation, and if Mr. Stromeyer's letter has 

 no other effect than to bring the subject once more forward it 

 will have done good service, but I should like to point out that 

 the second of the stars selected by him ought on no account to 

 be taken as a test of the feasibility of the method, since the 

 accurate discussion of the conditions shows that unless this is an 

 exceptionally remote system the velocity must be very small 

 indeed. For instance, assuming Johnson's parallax, viz. o"'20, 

 the relative velocity of the components amounted last year to 

 only o'6 miles per second. 



In the northern hemisphere the most favourably situated 

 binaries are 70 Ophiuchi, |-Urs3e Majoris, and, if Peters' orbit 

 represents the real motion of the pair, 61 Cygni ; while for the . 

 southern hemisphere special attention ought to be directed to 

 aCentauri and7-Coronae Australis. 



In Mr. Gore's Catalogue, referred to above, will be found all 

 the materials for determining when to observe any known binary 

 most favourably in this respect, and for deducing its parallax 

 from the measures obtained, and it ought to be borne in mind 

 before letting the subject sink back once more into oblivion, 

 that, other things being equal, this method is most likely to 

 succeed in the case of the most distant systems, where the 

 parallax is so small that the ordinary trigonometrical method 

 necessarily fails us, and that when the micrometer, the helio- 

 meter, and the stellar photograph break down, the spectroscope 

 will sound the further depths with ever-increasing facility. 



Dunsink Observatory, co. Dublin. Arthur A. Rambaut. 

 December 30. 



December Meteors (Geminids). 



These meteors were moderately abundant on the night of 

 December 12, which appears to have been a very favourable one 

 in regard to weather. The chief radiant point was observed in 

 the normal position very close to a Geminorum, and there was a 

 strong contemporary shower from a centre ea^t of )8 Geminorum. 



At loh. lom. December 12, a fireball estimated to be twice 

 as brilliant as Venus was observed by Mr. Booth at Leeds. It 

 moved rather slowly from 150^^ -{-43" to 188° -^ 41°, and divided 

 into two pieces at the finish, 



Mr. Wm. Burrows, of Small Lane, Ormskirk, writes to me 

 with reference to a meteorite which he observed to fall at a later 

 hour on the same night. He says the time was 6.52 a.m. 

 (December 13), and refers to the phenomenon as follows:— 

 " Seeing the meteor was coming to the earth I crossed the road 

 to where it appeared to be falling, and it fell about two yards 

 from me. When it struck the earth it made a noise like the 

 report of a gun ; it also went black instantly. While descending 

 it had a tail of fire about a foot long. It is if inch in diameter 

 oneway, and ijinch another, and one inch thick." 



Mr. Burrows sends drawings of the object, and it being still 

 in his possession it is hoped the matter may be suitably investi- 

 gated. Should it prove a veritable meteorite one interesting cir- 

 cumstance in connection with it will be that its descent took 

 place concurrently with the shower of Geminids. 



It is significant that December 9-13 constitutes a well-defined 

 asroliiic epoch, rendered memorable tiy the fall at Wold Cot- 

 tage, Thwing, Yorkshire, on December 13, 1795, and by many 

 others, such as that at Massing, Bavaria, December 13, 1803, at 

 Weston, Connecticut, U.S.A., December 14, 1807 ; at V/iborg, 

 Finland, December 13, 1813 ; at Ausson, France, December 

 9, 1858 ; at Baudong, Java, December 10, 1871, &c, 



Bristol, January i. W. F. DeNxNING. 



The Earth's Age. 



As Dr. Wallace (Nature, p. 175) trusts " that on further 

 consideration " I shall "admit that" my "objection is invalid," 

 it is evident that I have failed to make clear to him my argument 

 showing that his data do not warrant his conclusion. 



He overlooks the fact that a thickness of 177,200 feet of 

 sedimentary rocks is, standing alone, a perfectly indefinite 

 quantity ; to make it definite it must have a definite area. 



As he mentions no area for it we are justified in assuming thai 

 he means the land area of the globe, whereas his calculation 

 is made as though area were not of the essence of the problem, 

 in short, as if the formation of a pile of sediment 177,200 fee: 

 thick, of no matter what area, were the problem. 



NO. I 2 10, VOL. 47] 



