204 



KNOWLEDGE. 



[September 1, 1900. 



15. The spectrum of this star is said to l)e " com- 

 posite." 



2'2. One of the stars in the Soutliern Cross. 



23. Sjjcctrum accoi'ding to Ellery. 



35. This star was estimated 3.0 at Cordoba, and may 

 possibly be variable. Sir John Hcrschel made it 2.11. 



44. This star is red and a suspected variable. 



50. Spectrum according to Pechiile. 



53. This star has licen suspected of variation. 



54. Spectrum said to be " composite." 



55. This is the standard star of the photometric 

 catalogues, except the Revision of the H.P., in which 

 the comparison star is X Ursse Minoris, magnitude 6'57. 



60. A suspected variable star. It was rat-ed of the 

 first magnitude by Al-Sufi in the 10th century. 



G3. This star is a variable, but has no regular period. 

 The variation is from about 2.2 to 2.8, so that when 

 at its minimum light, it is not among the hundred 

 brightest stars. 



()6. The famous variable star. The variation is from 

 2.3 to 3.5, so that at minimum it I'etires for a few hours 

 from the list of " hundred brightest stars." 



72. A suspected variable star. 



73. A suspected variable star. 

 76. A suspected variable star. 



79. There is considerable difference of magnitude 

 lictween the H.P. and the Revision of the H.P. The 

 star was estimated 2.6. at Cordoba. 



82. Spectrum with hydrogen F line bright according 

 to Bailey. 



83. The spectiaim is said to be " composite." 



84. A known variable star which varies from about 

 2.2 to 2.7, but with no regular period. 



91. Allowing for difference of scale there is con- 

 siderable discrepancy between the Oxford and Potsdam 

 measures which suggests possible variation of light. 



The lowest magnitude given in the list is 2.72. The 

 following stars are brighter than this in the Revision of 

 the Harvard Photometry : — • 



li. m. 



a Columbw ."3 36 S. 34 8 2-55 S.M.P. 274 



S Leonis 11 8 8 N. 21 4 2-68 H.P. 275 



/JLnpi 14 52-0 S. 42 44 2 68 S.M.P. 274 



(3 Libr» 15 11-6 S. 9 1 266 H.P. 274 



/3 Scorpii 15 596 S. 19 31 270 H.P. 2 91 



Z Opbiuchi 16 817 S. 10 22 2-64 HP. 284 



Of the hundred stars in the list, 47 p^re north of the 

 Equator and 53 south, so that the 100 brightest stars 

 are pretty equally distributed in each hemisphere, with 

 a slight preponderance in favour of the southern hemi- 

 sphere. 



I find that of the 100 stars in the list, no less than 

 58 lie in or near the Milky Way, a remarkable fact 

 considering that the Galaxy does not — at most — cover 

 more than one-fourth of the area of the star sphere. 



With reference to spectra, there are 51 of the I. 

 type (including those of the " Orion type "), 34 of II. 

 type, and 7 of type III. Of the stars lying in or near 

 the Milky Way, there are 32 of type I., and 19 of 

 type II. This shows a marked preponderance of bright 

 Sirian stars in the Galaxy. 



It is, I think, a popular idea that the stars forming 

 the Southern Cross are some of the very brightest in 

 the heavens, but this is quite a mistake, as the brightest 

 of them, a. Crucis, is only 14th in the above list, the next, 

 /3 Cru(-is, is No. 22, the next, y Crucis, is No. 23, while 

 the fourth star, 8 Crucis, is not included in the first 

 hundred brightest stars, its magnitude' being only .3-08. 



H cttcr g. 



[The Editors do not hold themselves responsible for the opinions 

 or statements of correspondents.] 



HOT AND DRY SUMMERS. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — Distinguishing each of the last 60 summers 

 at Greenwich as either hot or cool, or as dry or wet 

 (by relation to the averages), it may not be too obvious 

 to remark that hot summers arc not all dry, nor cool 

 summers all wet. The following classification shows 

 this: — 



Hot and dry summers ... ... 53 



Cool and wet... ... ... ... 19 



Cool and di7... ... ... ... 12 



Hot and wet... ... ... ... 6 



80 



Let us arrange these 23 hot and dry summers in ten 

 groups, according to their positioji in a decade ; those 

 of years ending in 1 together, those of years ending in 

 2 together, and so on ; and represent each summer by 

 a dot at level corresponding to the temperature. (The 

 rainfall relation is not indicated in each case ; it will 

 be understood that all those summers had less rain than 

 the average.) 



/ 2 3 -^ 6' 6^ y ^ ^ 



6S- 



» o 



— • • e - 



• • , . ♦ 



Hot and Di'y Summers. 



In this rough diagram we might note the following 

 among other points : — 



1. The five hottest dry summers (64° and over) are 

 all in the years ending 6 to 9. 



2. Of ten summers over 63°, nine are in the decade 

 half 6 to ; and only one in the other half, 1 to 5. 



3. The years ending 6, 7, and 8 have four times as 

 many hot dry summers as those ending 1, 2, and 3 

 (12 to 3). 



4. The summers of years ending in 7, are all hot and 

 dry except one (1867). 



These facts might perhaps be found useful in fore- 

 casting. Alex. B. MacDowall. 



CRESCENT-SHAPED IMAGES OF THE SUN 

 DURING THE ECLIPSE. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — If you look under a tree when the sun is 

 shining you will see that where the sun finds its way 

 through the branches all the small spots of sunshine on 

 the ground are of a circular or oval shape. This is due 

 to the fact that the interstices between the leaves act 

 like the lens in a camera obscura, or perhaps to be 

 more accurate, they may be said to act like the pinhole 

 in the front of a pinhole camera, and they therefore 

 really project small images of the sun on the ground. 



The curious thing is that whatever the shape of the 



