November io, 192 i] 



NATURE 



351 



fitted those on the tracing, thus eliminating the effect 

 of the tilt of the aeroplane. When sensitised paper 

 was substituted for the tracing, the print ob- 

 tained was free from distortion, and was used for 

 plotting the map. 



Messrs. Macmillax and Co., Ltd., are issuing 

 immediately vol. i of "The Palace of Minos," a com- 

 parative account of the successive stages of the early 

 Cretan civilisation, as illustrated by the discoveries 

 at Knossos, by Sir Arthur Evans, price six guineas 

 net. The volume deals with the Neolithic and Early 

 and Middle Minoan Ages. It will be found to be an 

 indispensable preliminar}- to the study of Mycenaean 

 Greece, the culture of which is the outgrowth of the 

 earlier Minoan stages of Crete. 



Sir William Tildf.n and Prof. J. C. Philip are 

 editing for Messrs. G. Routledge and Sons, Ltd., a 

 new series entitled "The Twentieth-Centurj- Chemis- 

 try," the aim of which is the production of readable 

 and interesting books which, without being exhaustive 

 monographs, will furnish advanced students of 

 chemistry with a complete survey of the present state 

 of knowledge and opinion in each branch of the 

 science. 



Messrs. G. Bell and Sons, Ltd., are to publish 

 at an early date a translation, by L. Taverner, of "An 

 Introduction to the Study of Metallography and 

 Macrography, " by L. Guillet and A. Portevin. The 

 work will contain an introduction by Prof. H. C. H. 

 Carpenter. 



Our Astronomical Column. 



The French Wireless Ti.me-Signals. — ^These 

 signals are now so widely used by astronomers for 

 time-determination that it is well to direct attention 

 to an alteration which is announced in Circiilaire 

 Xo. 4, Bureau Internationale de VHeure. The signals 

 have hitherto been sent out at definite mean times ; 

 but the time is determined by meridian transits of 

 block-stars, which necessitates the use of a sidereal 

 clock, the error of which must be determined, and 

 that of the mean-time clock inferred by comparison. 

 It "is now announced that, in order to avoid this 

 transformation, beats i and 300 of the rhythmic 

 signals will be sent according to Greenwich 

 sidereal time, and the interval between the beats will 

 be 49 '50 of a sidereal second (roughly 44/45 ^^ ^ mean 

 second, instead of 49/50 as formerly). 



A detailed list of the mean times of the signals, 

 both old and new, and of the nature of the emissions 

 used in each, is given in the circular; there are 

 several changes. It is clear that a signal cannot be 

 sent both at a constant mean time and a constant 

 sidereal time : a different sidereal minute will be con- 

 cerned event' day. For some time after the change 

 the signals will be preceded by the words " sidereal 

 time," but it is not clearlv explained how the actual 

 sidereal minutes will be made known. 



The new system will come into use on November 15, 

 and will be experimented on up to the time of the 

 meeting of the International Astronomical L'nion, 

 when the question will be further discussed in the 

 light of the experience gained. 



Proper Motions of Long-period Vari.able Stars. — 

 Astronomical Journal, Nos. 784 and 791, contain deter- 

 minations of the proper motions of thirty-seven long- 

 period variable stars made at Mount Holyoke College 

 bv Misses Young, Farnsworth, and Jenkins. Two 

 series of plates were taken, the time-interval ranging 

 from nine to nineteen years. The proper motions are 

 referred to the faint background stars, which were 

 previously tested with a stereo-comparator, to exclude 

 any that showed appreciable motion. 



There is thus a certain amount of systematic shift 

 ill each field, arising from the solar motion, but it is 

 unlikely to exceed 001 " per annum in anv case. The 

 deduced annual motion for each star is : — RR 

 Androm., 0060"; Y Androm., 0021*; T Camelop., 

 0-016"; V Orion., 0028"; Y Monoc., 0031"; R 

 Gemin., 0022'; T Gemin., 0-029'; U Cancri, 0019*; 

 S Hydrae, 0037''; T Hydrae, 0021''; T Virg., o-oii"; 



XO. 271 s, VOL. 108] 



S Sagittar., 0013*; x Cyg-- 0038*; Z Cyg., 0018'; 

 W Capric, 0-027"; T Delph., 0023"; RR Aquar., 

 0052' ; S Ariet., 0091" ; R Ceti, 0022'' ; V Gern., 

 0040'; RU Here, 0-006* ; S Scorp., 0-037"; W Ophi., 

 0-030' ; RS Here, 0042"; SY Cyg., 0-030"; Z Aquil., 

 0023"; S Peg., 0066"; S Aurig'., 0042^; U Puppis, 

 0-039"; V Leo., 0023"; V Lib., 0056"; U Serp., 

 0049" ; Y Aquar., 0-038" ; T Capric, 0-014" ; U Aquar., 

 0-020' ; and R Peg., 0-038". 



The mean value is 0-032', implying distances of the 

 order of 100 parsecs. The sun at this distance would 

 have magnitude 10-5, so that the stars in question 

 have absolute magnitude (at maximum) somewhat 

 brighter than the sun's. They are, therefore, not 

 extreme dwarfs, but neither are they extreme giants of 

 the type of Betelgeux. The only long-period variable 

 with a considerable proper motion is Slira Ceti, for 

 which Boss's value is 0-237*. 



The Last Gt,\ciAL Epoch. — The Ice ages have an 

 astronomical aspect, so that reference may be made in 

 this column to a paper by Mr. C. E-. P. Brooks 

 (Quarterly Journal R. Met. Soc., July, 1921) which 

 assigns the date 30,000 to 18,000 B.C. for the last great 

 glaciation in North-West Europe (Ireland, Scotland, 

 Scandinavia, and the Baltic). Some remains of glacia- 

 tion continued until 6000 B.C. ; after some intermediate 

 phases the date 1800 B.C. to a.d. 300 is assigned to 

 the Peat-bog Phase, when the climate was cooler and 

 moister than at present. Thes changes are attri- 

 buted chiefly to alterations of elevation ; increased 

 elevation has the double effect of producing glaciation 

 on land and of closing the Straits of Dover and other 

 channels for the warm currents from the Atlantic. 

 Mr. Brooks also assigns considerable weight to the 

 1800-year cycle in tide-generating force announced bv 

 Mr. O. Pettersson. But it is veni- doubtful whether 

 this cycle will explain any appreciable climatic 

 changes. It does not mean that all the tides are 

 higher at one of these 1800-year maxima, but merely 

 imp'ies that there are a few tides in the vear verv 

 slightly in excess of those at other epochs, just as there 

 are total solar eclipses of maximum duration at some- 

 thing like the same interval. 



Since Mr. Brooks gives evidence of an approach to 

 simultaneity in climatic changes in Europe and 

 •America, some cosmical cause is indicated ; but the 

 suggestion of a long-period variation in solar output 

 (analogous to the shcwt-period variations announced 

 ijv Mr. Abbot) seems more hopeful than the tidal 

 cycle. 



