December 1, 1898.] 



KNOWLEDGE. 



279 



I differ from Mr. Low aa to Chaucer's own belief in 

 astrology. He writes olt in detail, as I showed. But I 

 think he no more believt in it than did Flamsteed, who 

 yet drew a horoscope t determine a fortunate hour for 

 founding Greenwich Obs vatory. or Sir Walter Scott, who 

 yet showed a perfect ac laintance with its principles in 

 " Guy Mannering." — E.V'ai.ter Maunder.] 



THE GICAt' SUN-SPOT. 

 To the F.dirs of Knowledge. 

 Sirs, — With referent to Mr. Maunders interesting 

 article on this subject i the October number, I beg to 

 send you enclosed a dra^ng 1 made of the spot when very 

 near the Sun's eastern 1 ib, September 'id. 6h., and other 

 drawings September di 2h., and September id. Ih., all 

 G. M. T. 



Sunspot in 3 edge. Power 120. 



Kdge of 3i cuts the penumbra ? 



\ 



Sept. 2ii(l, 1 p.m. Sept. 3rd ■ a.m. Sept. 4th, 8 a.m. ISOS. 



They were taken witlk four -inch equatorial and a solar 

 prism, and are therefor subject to the inversion peculiar 

 to such prisms ; this lay be rectified by viewing the 

 reflection of the drawit i in a looking-glass. The power 

 used was one hundred \d twenty. The last drawing by 

 mistake makes the spot little too short. 



Jamaica, M.wwell H.u,l. 



October 2-ith, Ibs. 



VAl ABLK STARS. 

 To the E tors of Knowledge. 



Sirs, — I think there no real point in dispute between 

 me and Col. Markwick jut I may perhaps suggest that 

 some variables may be eally of the eclipse-type, though 

 not usually so classed. 



If the obscuring bodj i a close satellite and the obscured 

 star is very distant, thcosition of the earth in its orbit 

 would practically make o difference in the phenomena. 

 But suppose that the bscuring body is a very distant 

 satellite, or belongs to iifierent system, but happens to 

 be almost in the direct line between the earth and the 

 bright star, the amoun of obscuration might depend on 

 the earth's position ij its orbit, and the period of the 

 variable star would be ery nearly one year. Now, as a 

 matter of fact, the nun er of variable stars with a period 

 of nearly one year seen larger than chance wLU account 

 for. Is the excess due i this cause ? 



With ordinary eclips variables we may expect, on the 

 tidal theory, a slow inc ase of the period, accompanied by 

 a slow diminution in tl amount of the variation. But at 

 the same time the mc ments of the sun and the star 

 through space would lobably render the eclipse either 

 more or less central an thus compUcate the phenomena. 



Whether the cause v ich I have suggested will afford 

 the true explanation of hat I may call annual variables, 

 will I think chiefly dep^d on the result of observations 

 as regards their spectnat different periods. 



W. H. S. Mo.NCK. 



VARIABLE STARS IN GLOBULAR CLUSTERS. 



By Miss Ag.ves M. Clerke, 



Author of " The System of the Stars," " A Popular History 



of Astronomy during the Nineteenth Century," etc., etc. 



GLOBULAR clusters are, perhaps, the most fasci- 

 nating of telescopic objects. Their silver radiance 

 delights the eye ; the mystery of their constitution 

 allures thought. What, we instinctively ask 



ourselves, is the reality corresponding to the 

 strange and beautiful appearance of " balls of stars " ? 

 Are the luminous particles composing them sunx in any true 

 sense '? What are their mutual relations '? Is their aggre- 

 gation destined to be permanent ? Do they form stable 

 systems, or merely temporary societies undermined by 

 forces tending towards dissolution ? Some indications on 

 these points have been gathered, but definite information 

 is still to seek. Only within the last few years, indeed, 

 have the objects in question been brought within the 

 scope of organized research. 



There need be no hesitation, however, in atHrming that 

 swarming stars belong to the same cosmic family as 

 solitary stars — that they are spherical masses of intensely 

 heated matter, radiating into space by means of suitably 

 adapted photospheric apparatus. But they are unlikely 

 to be xolar suns. Many are sensibly, probably all are 

 sub-sensibly nebulous. They stand, then, presumably at 

 an earlier stage of development than our own luminary, 

 and may be greatly less dense proportionately to their 

 brilliancy. The nature of their spectra ought here to 

 prove of decisive import. Too dim for separate examina- 

 tion, they, nevertheless, reinforce each other sufficiently, 

 where the stars run together in the central " blaze," to 

 give intelligible results with powerful appliances. The 

 early efl'orts to obtain them, made by Sir William Huggins 

 and Dr. Vogel, at a time when no adequate means were 

 available, can now at last be carried out with good promise 

 of a successful issue. 



In our present ignorance of their distance from the 

 earth we are unable to determine the scale of these 

 jostling suns. A rough calculation, however, shows that 

 an enormous remoteness would correspond to standard — 

 that is, to solar light-power. 



The grand southern cluster ;,• Centauri has been 

 thoroughly investigated from one hundred and fifty 

 negatives taken at Arequipa. Prof. Pickering may well 

 call it " the finest in the sky. ' He adds that it lies just 

 within the border of the MUky Way, and appears to the 

 naked eye as a hazy star of the fourth magnitude. It has 

 a diameter of about forty minutes. Over six thousand 

 stars have been counted on one of the photographs, and 

 the whole number is much greater. ' . If we assume it to 

 be seven thousand, then the average lustre of the purtides 

 contained in a single 'Irop of light equivalent to a fourth- 

 magnitude star comes out at 13-6 magnitude. But our own 

 magnificent orb, actually of minus 25*5 magnitude (accord- 

 ing to Pickering's estimate', if removed so far as to have 

 a parallax of only one-hundredth of a second, would still 

 take eleventh stellar rank. Only a remoteness three-and- 

 a-third times greater stUl. implying a light journey of over 

 eleven hundred years, could render it faint enough to pass 

 in the crowd of the assemblage in the Centaur. The 

 possibility that it may be plunged thus deep in the void 

 cannot be gainsaid, since the spatial unit fixed by measure- 

 ments of the parallactic pendulum-swing of the nearer 

 stars has yet to be appUea to the galactic world in aU its 

 length and breadth ; but, as Kepler said, " the pill is a big 

 one to swallow." 



* Harvard College Observatory Circular, No. 33. 



