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NATURE 



[March 6, 1919 



tion, when ready for use, \s. per litre. Fortu- 

 nately, however, it retains its digestive action for a 

 fortnight before the ferment is destroyed by bacteria, 

 but its action becomes slower and slower. 



In the Gardeners' Chronicle of February 8 Mr. 

 VV. B. Brierley, writing from the recently estab- 

 lished Institution of Pathological Research, Rotham- 

 sted, discusses the question of the diseased areas on 

 orchid-leaves known to horticulturists as "orchid spot." 

 This, he points out, is not a single and specific 

 disease, but a congeries of diseases, all little under- 

 stood and urgently in need of detailed investigation. 

 From the casual examination of diseased specimens 

 during the past two or three years Mr. Brierley has 

 recognised seven distinct types of disease. Of these 

 it is highly probable that four are the result of the 

 action of parasitic organisms, one of local chilling 

 of the leaf-tissues, one probably of atmospheric 

 poisoning, and one of some other physiological de- 

 rangement of the protoplasm, due probably to unsuit- 

 able cultural conditions in the plant's physical en- 

 vironment. A continuous and intensive study of 

 "orchid spot" would doubtless show that the seven 

 diseases are but a few of the many covered by this 

 name. At present all these diseases are lumped 

 together as " orchid spot," and horticulturists en- 

 deavour to control a disease of physical causation by 

 a fungicidal spray, or a fungal epidemic by regulating 

 to a nicety the temperature of the water supply. 

 There is needed a detailed investigation of this group 

 of diseases, a critical experimental study of the physio- 

 logical relations of the plants to their environment, an 

 understanding of all the complex hygienic factors 

 involved, and a thorough elucidation of the life- 

 histories and biological relations of the pathogenic 

 organisms which may be present. Only on such a 

 foundation can a rational scheme of prophylactic and 

 therapeutic treatment be based. 



The Monthly Meteorological Chart of the East 

 Indian Seas for February, issued by the Meteorological 

 Office, shows in great detail the various meteorological 

 data. Winds are given in an extremely intelligible 

 and useful form for navigators, and aircraft can use 

 much which has been primarily prepared for the sea- 

 man. The wind-zones show for each 5° of latitude by 

 5° of longitude both frequency and strength. The 

 limits of the trades and monsoons are shown on 

 the face of the chart, and tracks of some cyclonic 

 storms are given. Results for the several elements 

 are obtained from recofds extending over a period of 

 about sixty years. Ice information is given on the 

 back of the chart, and navigators voyaging in high 

 southern latitudes will find the information very 

 helpful in avoiding a common source of danger. 

 There is a desire on the part of the Meteorological 

 Office for captains who are interested in meteorology 

 to assist in the work by observing for the Office. 

 Naturally, the organisation has been seriously inter- 

 rupted by the war, so that the assistance of voluntary 

 observers is now the more urgent. The series of 

 charts for the several months shows in the clearest 

 possible manner the change of monsoon over the area 

 of the sea embraced. 



OUR ASTRONOMICAL COLUMN. 

 The Order of the Planets. — In the oldest cunei- 

 form inscriptions the planets are given in the order 

 Jupiter, Venus, Saturn, Mercury, Mars {vide " Encycl. 

 Brit.," eleventh edition, vol. ii., p. 796, "Astrology"). 

 Dr. Herbert Chatley writes from Shanghai to point 

 out that if we calculate the total gravitational force 

 between the sun and each planet (viz. product . of 



NO. 2575, VOL. 103] 



masses -^square of distance) we obtain results which 

 in order of magnitude agree with the list above. 

 With the latest values of the planetary masses the 

 numbers are : — 



Mercury, 0-24. 

 Venus, 1-58. 

 (Earth, 100.) 



Mars, 005. 

 Jupiter, 11-76. 

 Saturn, 104. 



This cannot be anything more than a coincidence, but 

 it is sufficiently curious to justify mention. Dr. 

 Chatley notes that if by chance the ancients had 

 possessed the necessary knowledge, they would have 

 grouped the planets, not by the simple attractions, 

 but by their tide-raising power, which would have 

 involved the inverse cubes of the distances. 



Cepheid Variables. — ^The Observatory for February 

 contains a letter by Mr. J. H. Jeans on the Cepheid 

 problem. Mr. Jeans gives the following functional 

 formula for the Cepheid light variation : — 



a cos nt + bf[n{t-ri)\, 



where a, b, jj are adjustable constants, and / is the 

 same function for all stars. The spectral type follows 

 the second term of the expression fairly closely, maxi- 

 mum value of / corresponding with early or B type, 

 minimum value with late or K type. 



The graph of the function / shows a steep rise 

 followed by a much less steep and approximately 

 exponential descent; its period is the same as that 

 of the first term in the formula. This latter fact leads 

 the author to ihe conjecture that the o cos nt term 

 arises from the rotation of a single elongated body, 

 and the bf term from an explosion which occurs in a 

 particular orientation of the body, this explosion pro- 

 ducing the change in spectral type. He shows that 

 Mr. Phillips's Group I. of light-curves would be ex- 

 plained by one explosion per rotation, and Group II. 

 by two explosions per rotation. There is, how- 

 ever, a difficulty in picturing a mechanism that could 

 produce explosions in fixed orientations, for any 

 external disturbing body would necessarily be chang- 

 ing Its orientation. 



Variation of Latitude. — The observatories of 

 Mizusawa, Carloforte, and Ukiah (all in N. lat. 

 39° 8') continued their series of latitude observations 

 throughout 1917- The results are discussed by 

 B. Wanach in Ast. Nach., No. 4969. The minimum 

 latitude in the meridian of Greenwich was — o»i4" at 

 the end of March, the maximum +016" early in 

 November. The track of the pole is considerably 

 more contracted than in the two preceding periods. 



Issei Yamamoto contributes a paper on the 

 "Kimura" or "z" term in the latitude variation 

 (Proc. Tokyo Math. Phys. Soc, second series, vol. ix., 

 No. 17). He has made observations to test Prof. 

 Shin jo's suggestion that the term arose from an 

 annual term in the distribution of temperature in and 

 above the observing-room, and consequent dis- 

 symmetry in the refraction. 



He made a specially designed observing-room, with 

 precautions to equalise the temperature of the air 

 above it, and found that the "z" term was greatly 

 reduced. His results thus tend to confirm Shinjo's 

 suggestion. 



The values of the variation of latitude that are 

 adopted for the Greenwich reductions are deduced 

 from the results obtained with the Cookson floating 

 telescope. They are ready long before the publica- 

 tion of the results at the international stations, and 

 it Is found that thev do not differ much from the 

 latter. 



