112 



KNOWLEDGE. 



[May 1, 1896. 



the rise from 60 to 7'4 magnitude occupying nine, the 

 corresponding descent twelve hours and twenty minutes. 

 Spectroscopic motion may, then, here prove extremely 

 rapid. Nevertheless, since it represents only the pro- 

 jection upon the visual plane of the orbital velocity, 

 the verdict of experience as to its quantity in any particular 

 case cannot be anticipated, unless by a bare surmise. 

 Stars, indeed, presumably exist which, although judged by 

 analogy to be swiftly circulating binaries, will show no 

 trace of line-displacements, simply because their plane of 

 revolution is approximately perpendicular to the line of 

 sight. Such examples would be particularly instructive, 

 as illustrative of light-variation where eclipses could not, 

 by any contrivance of the imagination, be brought into 

 play. 



Spectroscopic binaries fall into the three divisions ; of 

 eclipse-stars, of which eleven are now known ; variables 

 without an eclipse, such as /3 Lyrse and S Cephei ; and 

 stars of sensibly constant brightness, exemplified by 

 a Virginis and /3 Auriga. Not improbably, however, the 



%ttttv. 



Fig. 2. — Algol in full light. In Curres II. and III. the crosses represent the annual means of 

 Pannekoek's observations; the dots in I., II., and III. standing for Plassmanu's corresponding results. 



last description may prove, on closer inquiry, to be subject 

 to inconspicuous fluctuations, similar to those by which 

 Algol is apparently affected when uneclipsed. Fig. 2 

 shows the remarkable curves drawn by M. Plassmann 

 (Ili-dliKchtwu/m Vcraivl. Sterne, IV., 1H!J5) to represent his 

 observations of this star during the years 1891-4, which 

 have been to a great extent confirmed by those of 

 M. Anton Pannekoek at Leyden. It will be noticed that 

 the changes indicated are themselves changeable. Another 

 Algol-variable, U Coronw, was perceived by Schonfeld to 

 waver in brightness, apart from its regularly recurring 

 phases ; but little or no attention has, for the last score of 

 years, been paid to the details of its light-curve. In these 

 stars, accordingly, we have an eclipse with complications ; 

 in others, we find complications without an eclipse. 



[The Editor does not hold himself responsible for the opinions or 

 statements of correspondents.] 



* 



THE WINDS OF MAES. 



To the Editor of Knowledge. 



Sir, — M. Camille Flammarion, writing on " The Circula- 

 tion of Water in the Atmosphere of Mars," states there is 

 on that planet " nothing analogous to our trade winds or 

 to the reijhnc of predominant winds which govern our 

 terrestrial climate." This is an error. The rapid inunda- 

 tions over immense tracts of land must be caused by 

 considerable heat rapidly melting the snow in the summer; 

 the polar zone then becoming warmer, the prevailing 

 winds would be towards the pole, taking back the water in 

 the shape of vapour to be again deposited in the state of 

 snow, in the winter, at the poles ; otherwise, how does he 

 account for the annual accumulation of snow at the poles ? 



Yours truly, 



A. E. Whitehouse. 

 30, St. George's Place, 

 London, S.W., 

 April 8th, 1895. 

 [M. Flammarion certainly 

 did not intend it to be 

 understood that there were 

 absolutely no winds or air- 

 currents on Mars. To such 

 an idea Mr. Whitehouse's 

 objection, that there could in 

 that case be no accumulation 

 of snow round the poles, 

 would be fatal. But the 

 feebleness of the action of 

 gravity at the surface of Mars 

 will necessarily cause all air- 

 currents to be much more 

 languid than on the earth. 

 The Martian trade winds will 

 not be trade winds as we 

 know them here, but will be 

 merely steady but very gentle 

 breezes. On the other hand, 

 the vertical currents will be 

 even more restrained, and it 

 will be easier for moisture - 

 laden currents from the 

 equator to travel as upper 

 currents into the polar regions 

 than it is here on the earth, 

 in spite of their moving so 

 much more slowly. 



E. Walter Maunder.] 



An egg of the great auk, or gare fowl {Alca iinpennis), 

 was sold by auction on the 2.3rd of April, at Mr. Stevens' 

 rooms in King Street, Covent Garden. The bidding was 

 not very brisk, the price realized being only 180 guineas. 



A good stuffed specimen of the great auk was also put 

 up ; 3.50 guineas was the highest bid, but the bird 

 remained unsold. This specimen belongs to Sir F. Milner, 

 and was sold to him by Graham, of York, who stated that 

 it was taken in the Orkneys. Prof. Newton believes that it 

 was originally given by Gardner to the Rev. R. Buddicorn, 

 of Smethcote, Shrewsbury, and purchased from him by 

 Graham ; also that it comes from the Rock of Eldey, off 

 the coast of Iceland. 



