Septembek 1, 1898.] 



KNOWLEDGE. 



205 



VARIABLE STARS OF SHORT PERIOD. 



WHOEVER will make a careful examination of 

 the brightness of a large number of stars, 

 either in the sky, or, better, as photographed 

 upon different plates, will be impressed with 

 the vast number which show no perceptible 

 variation. The discovery of variable stars is greatly aided 

 when we are able to make a suitable selection for examina- 

 tion, either from their spectra or from their presence in 

 clusters. Visually, we can never be sure that all the 

 variables in a given region have been found, however 

 carefully we may study them. Photography brings this 

 problem more nearly within our reach, and a partial 

 solution of it is illustrated in the accompanying figure. 

 A photographic telescope was constructed having as an 

 objective a Cooke anastigmatic lens with an aperture of 

 2-6 cm. and a focal length of 33-3 cm. This telescope was 

 mounted equatorially, and the lens was alternately exposed 

 and covered for intervals of exactly ten and fifty minutes 

 by an electrical attachment. The polar axis of the 

 mounting was displaced and the rate of the driving clock 

 was increased, so that the successive images should be 

 slightly separated. An eight-by-ten photographic plate was 

 exposed in this instrument on April 2l3t, 1898, and eight 

 successive images were obtained, the Greenwich mean times 

 of the middle of the exposures being 13h. 49m., 14h. 49m., 

 15h. 49m., IGh. 49m., 17h. 49m., 18h. 48m., 19h. 48m., 

 and 20h. 48m. The plate covered a region about thirty- 

 three degrees square, whose centre was R.A. = lh. 2m., 

 Dec. = -f76'6^ The images of the stars in the corners 

 of the plate were sufficiently good when visible to show 

 very slight variations in light, but owing to their increased 

 size the faintest stars were not shown. The greatest loss 

 amounted to about one magnitude. If, now, any variable 

 star having a period of less than fourteen hours was con- 

 tained in this region, it is probable that at least one 



maximum and one minimum would be photographed. 

 The figure represents a portion of the plate described 

 above, enlarged ten times to a scale of G0"=0'1 cm., and 

 covers about one square degree. It therefore represents 

 one- thousandth of the entire plate, the size of which on 

 this scale would be two metres, or nearly seven feet square. 

 The entire sky, from the north to the south pole, could be 

 covered by forty such plates, and it is proposed to do 

 this as soon as the best method of taking the plates has 

 been determined. The arrow indicates the variable star 



U Cephei, and its photometric magnitudes at the times 

 the eight images were taken were 7*5, 8*1, 8-9, 9"1, 

 9'1, 8-3, 7-0, and 7-2. The three stars above it are 

 -f8r 30', +81 27', and +81° 29', which have the photo- 

 metric magnitudes 7'9, 8-.5, and 8-G. To separate the 

 successive images various methods have been tried. The 

 best of these seems to be stopping the driving clock for a 

 few seconds every hour. By the above plan we hope to 

 secure a complete list of all variable stars of short period 

 brighter than the ninth magnitude at maximum whose 

 variation exceeds half a magnitude and whose period is 

 less than a day. Doubtless, many other variable stars of 

 longer period, and stars of the .\lgol type, may also be 

 incidentally found. 



Edwabd C. Pickering. 

 Harvard College Observatory. 



CANTERBURY 



THE ASTRONOMY OF THE 

 TALES." 



By E. Walter Maunder, f.r.a.s. 



THERE is one subject of which men never tire. 

 They are always willing to be told of the way in 

 which other men in different circumstances, in 

 other lands, or in past ages, lived ; of their habits 

 and thoughts. Those who can tell us with certainty 

 and vividness these things about other men will always 

 claim our attention, and because of aU such narrators he 

 is one of the freshest and most natural, old " Dan Chaucer, 

 the first warbler," as Tennyson so aptly calls him, will 

 never lack an audience. 



There are other reasons for his popularity. 



" Oh to be in EnjjlaiKl, 

 Xow that April's there," 



was Browning's wish, and Chaucer ever takes us to 

 England in the freshest, fairest blossom of a spring-time, 

 always young. A free-hearted contentment possesses him 

 at all times : — 



■'SutBce thee, thv good, though it be small." 



But more frequently this broadens out into a frank joyous- 

 ness that refreshes us stiU, five hundred years after he has 

 gone to sleep. 



" Unto this day it doth mine hertS boote, 

 That I have had my world as in my time." 



It is not, however, with Chaucer as a poet, or as a 

 shrewd, observant kindly man of the world, that I am now 

 concerned. Like one of his friars whom he scathes so 

 sharply, yet so amusingly, I have to keep within my 

 " lymytatioun," and to ask him, not for the sweet scent of 

 the hawthorn, nor for the joyous notes of the woodland 

 birds, but for any information which he may have to give 

 as to the astronomy of his time. 



From a poet so natural, so absolutely unpedantic, living 

 long before the invention of the telescope and the revival 

 of learning, and in a poem, the subject of which is the 

 wayside talk, and free blunt banter of ordinary folk, one 

 would not naturally expect to find a single astronomical 

 allusion, nor, if we found any, that they should be 

 accurate. Yet even in Tennyson, by far the most scientific 

 of our modern poets, there are scarcely more astronomical 

 allusions than there are in Chaucer. 



On the first day of the month just past — " Saint Lubbock's 

 Day " — a far greater pilgrimage than that which was " per- 

 sonally conducted " by the stout host of the Tabard Inn, 

 set out from London and spread itself through Kent, in 

 much the same direction as their forefathers, half a 

 millenium before. But it may well be doubted if any of 



