October 24, 1895] 



NATURE 



629 



grisens), European, an Antarctic Skua [Stercorarius anlarcticus) 

 from the Antarctic Seas, presented by the Hon. Walter 

 Rothschild ; two Senegal Touracous (Corythaix persa) from 

 West Africa, presented by Mr. I. J. Roberts ; three Blackcaps 

 {Sylvia atrica/filla), a. W\g\A\T\ga.\e{Dauli(ts luscinia), British, 

 presented by Mr. Poynter ; a Wall Lizard {Laccria miiralis) 

 from Sicily, presented by Mr. A. M. Amster ; a Dwarf 

 Chameleon (Chamtckon pumiltis) from South Africa, presented 

 by Mrs. S. Jackson; two Squirrel Monkeys \Chrysothrix 

 uiurca) from Guiana, a Sjwtted Eagle (Aqtiila mrvia) from 

 India, three Weka Rails [Ocydronius aiislralis), four Tuatera 

 Lizards (Spheiiodon punclatus) from New Zealand, deposited ; 

 two CJrisons {Galiitis vettatd), a Coypu (Myopolainus coyptis) 

 from South America, two Western Boas (Boa occidentalis) from 

 I'araguay, purchased. 



OUR ASTRONOMICAL COLUMN. 



Si;.N-spoT OnsKRVATiONS IN 1894, — In 3. Separalabdnick aiis 

 der Vicrleljahrschrift dcr Naturforsckcjidcn Gesellschaft in 

 Ziiriili, Jahrgang 4, 1895, ^''- -'^- Wolfer brings together some 

 results relating to the sun-spot statistics made in Zurich and else- 

 where f<jr the year 1S94. The pamphlet opens with a deter- 

 mination of the constants for reducing the observations of each 

 observer to one scale. 



The mean observed relative number of spots for 1894 came 

 out as 78*0 as against 84^9 in 1893, showing a distinct 

 decrease. The secondary variations were also very prominent 

 during this year : further, between two very low minima 

 there occurred a j>rominent maximum lasting from May to July. 

 Nevertheless there was on the w hole a general decrease, making 

 it possible to dcteruiine the ejioch of the last important maximum. 

 Having plotted the relative number of observed sun-spots for the 

 three years 1892-94, and connected them together, the smoothed 

 curve indicated a maximum at l894'0. The length of the 

 elapsed period, that is, from maximum to maximum, became 



18940— i883'9 = 100, 



and the interval between the last minimum and the present 

 maximum 



1894 o — 1889 6 = 4'4. 



Dr. Wolfer makes a comparison of the sun-spot numbers with 

 the variations of the magnetic declination. Here there seems to 

 be a very good agreement, and the curves for both are very 

 similar. The epoch of the maximum magnetic variation, inde- 

 pendently determined, occurs in August 1893 or 18936, which 

 coincides ex.ictly with the secondary rise of the curve of relative 

 sp<it numbers. This secondary rise in the curve occurs just 

 before the time of maximum deduced from the smoothed curve, 

 and suggests rather that the former dale should represent the 

 chief sun-spot maximum. Dr. Wolfer, however, is not of this 

 opinion, and prefers to hold to the date gathered from the mean 

 curve. The pamphlet concludes with a tabular statement of 

 each of the observers' individual observations for the year 1894, 

 together with reference to the literature. 



Planetary rERTURB.vriON.s. — In No. 3312 of the Aslro- 

 noinische Nachridilcii, Prof. A. Weiler gives another paper on 

 the subject of long-period and secular perturbations. The 

 particular case considered is that of the disturbance of a 

 planet, having a me.in motion approximately twice that of the 

 disturbing planet, and is really a special case of the more general 

 problem of [ierlurbations already treated in earlier numbers of the 

 same journal. We cannot indicate here the mathematical 

 formuke which are given, and much of which would be un- 

 intelligible without the earlier papers, but attention may be 

 called lo one of his results. 



When tlie commensurabilily in the periods of the disturbed 

 and disturbing planets becomes very close, that is if 5 = i - 2;ii be 

 very small, where ^ is the ratio of the two mean motions, the 

 series by which the perturbations are expressed is notjconvergent, 

 and the prolilem is apparently insoluble. Such a result is 

 inconsistent with the regularly observed motions of the planets, 

 and therefore points to some error in the assumptions on which 

 the solution of the problem is founded. This error Prof 

 Weiler traces to the treatment as constant of the semi-axis 

 major of the dislurljed planet's orbit. The justice of this remark 



NO. 1356, VOL. 52] 



is illustrated by a reference to the arrangement of (he asteroids 

 in space, whose distribution offers peculiarities explicable on the 

 hypothesis that the mean daily motion is variable if the 

 approximation to commensurability oversteps a definite limit. 

 Taking a list of twenty-five asteroids, wherein the value of 

 5=1 -2^ is less than one-fifteenth, he shows that none have a 

 period giving a mean daily motion very^ approximately twice that 

 of Jupiter (598"-3). The mean daily motion of these twenty- 

 five lies between 562"'2 and 640"'2, but none come be- 

 tween 572" '6 and 6l4"'4 ; that is, the mean motions 

 separate on both sides of twice that of Jupiter. The force of 

 this illustration is somewhat im|)aired if the list be made lo 

 comprise those more recently discovered. The asteroids Nos. 

 332 and 381 have mean motions of 6o5"'5 and 6i3"'5, respec- 

 tively, and it should further be remembered that in the whole 

 list of asteroids, there are only five whose means approach the 

 lower limit of 562". This remark simply refers to the value of 

 the illustration, not to the accuracy of the fact it is called in to 

 support. 



The Syste.m of o Centairi. — The meridian measures of 

 the positions of a, and Oj Centauri, made at the Cape in 

 1879-1881 have l)een utilised by Mr. A. W. Roberts for a 

 determination of the relative masses of the two stars, and other 

 data connected with the system (Ast. A'aih. No. 3313). The 

 place of the centre of gravity for 1880 is given as R.A. 

 14I1. 31m. 27'537s.. declination - 60' 20' 20 '63 + o""l3 ; 

 proper motion in declination (1880) = + o"750 + o"'005 ; 

 proper motion in \<..\. (1880) = - 7"-29i + o'o32. For the 

 relative ma.sses of the two stars, the values derived are 51 to 

 49 ± 1/50 of the amount. 



According to the results obtained by Mr. Roberts, Oj 

 Centauri is very slightly heavier than the sun, while a, is 

 about two-hundredths lighter. Since Oj is now between 

 five and six times brighter than o,, it must have by far 

 the brighter surface. Taking a mean of the different values 

 which have been obtained for the sun's brightness in relation 

 to the stars, " it would appear that o, Centauri is as bright as 

 our sun, while a, is about five limes fainter.' o, Centauri is 

 accordingly some distance on the downward track from the 

 dignity of a sun to that of an ordinary planet : while a„ Centauri 

 is, as regards light, size, and mass, a twin-brother of our 

 sun." .Spectro.scopic observations «ill furnish another method 

 for determining the relative masses, but, in order to improve on 

 our present knowledge, the observations of velocities must be 

 accurate lo within one or two tenths of a mile per second. 



Holmes' Comet. — This comet, which has presented such 

 peculiarities both in its physical structure and the form of its 

 orbit as to make it one of the most remarkable comets of short 

 period, has been made the subject of an elalxirate investigation 

 i)y Dr. II. I. Zwiers. Taking into account the .action of Jupiter 

 and Saturn, but neglecting that of the Earth, to which, owing to 

 the great perihelion distance of the cornel, it cannot make any 

 close approach. Dr. Zwiers is led lo fix the date of the next 

 perihelion p<assage on .\pril 27, 1S99, and gives an ephemeris 

 commencing on February 16, 1898, ihe earliest date at which a 

 search is likely to be successful. The theoretical brilliancy is 

 then o'oo63, and when last seen in 1893, the brilliancy was ex- 

 jiressed by ooiiS. In .-Vpril and May, when the comet will be 

 well situated for observation in the southern hemisphere, this 

 latter quantity will be exceeded, and will approach that, that the 

 comet possessed in January 1893, when it underwent such a 

 remarkable change in its appearance. If the comet retains its 

 stellar-like character, the difficulty in detection will no doubt be 

 increased, but an early discovery is eminently desirable. 



ON THE HABITS OF THE h'EA, THE SHEEP- 

 EATING PARROT OF NEIV ZEALAND. 

 "T^HE kea, the mountain parrot of New Zealand (Ntslor iiota- 

 ■'■ bilis), h.is earned considerable notoriety from its remarkable 

 habit of attacking living sheep. It is commonly slated that the 

 natural food of this bird consists of insects, fruit, and berries ; 

 and that it has developed a taste for a carnivorous diet only 

 during the last thirty years. Mr. Taylor White, however, has 

 recently pointed out (Zoologist, .-Vugust 1S95) that the \-arious 

 statements on the habits of this biril have all been derived frora 

 secondhand information ; and, as the habitat of the parrot is on 

 the tops of .Mpine ranges, owners of sheep and shepherds who 



