562 



NATURE 



[July i, 1920 



fantastic; and, above all, of its pilots, that with the 

 skill and technique peculiar to tfteir craft they shall 

 combine a practical working knowledge of structure 

 and of machinery, of instruments and "wireless," of 

 meteorology and of navigation, which in other pro- 

 fessions would be the province of different specialists. 

 And this universality, as might be expected, is no less 

 characteristic of the appeal which aeronautics has 

 made to the man of science, who provides it with 

 fresh data ; so that it is not surprising to find that the 

 single committee of pre-war days has been compelled 

 to adopt a''policy of devolution, and that special sub- 

 committees have been formed to deal with problems 

 of such different scope as "scale effect," the_ investiga- 

 tion of accidents, internal-combustion engines, light 

 alloys, meteorology, atmospheric electricity, and new 

 inventions. 



The report abounds with indications of fields in 

 which further research is needed, and there seems 

 every reason to believe that this research will be 

 prosecuted with equal success under the auspices of 

 the newly constituted Aeronautical Research Com- 

 mittee. We learn with satisfaction that the demand 

 for the earlier technical reports has been vigorous 

 enough to justify the printing of a complete second 

 edition, since an opportunity is thus given for insert- 

 ing much more complete cross-references than were 

 possible when they first appeared. It is, perhaps, a 

 matter for some ' little regret that a more definite 

 lead has not been given in this direction by the present 

 report. We imagine that any reader whose interest 

 in the subject extends to the detailed reports of the 

 several sub-committees would .wish to have such 

 references to individual papers and their authors as 

 will enable him to find additional information on any 

 special point; moreover, an account so detailed, and 

 yet empty of names and references, may fail to im- 

 press what we believe is the secret of British 

 supremacy in aeronautics : that our official Committee 

 has interpreted its functions as being advisory rather 

 than executive, and has endeavoured to assist, co- 

 ordinate, and encourage research rather than to 

 originate and control it. 



No useful end would be served, and persp-ective 

 would be lost, bv abstracting from these excellent and 

 thoroughly condensed reports. Their range is verv 

 wide, extending from complete investigations, on both 

 the practical and theoretical sides, of such complex 

 evolutions, as "spinning" to researches on the pro- 

 perties of light alloys, the transmission of heat from 

 rough and smooth s'urfaces to passing currents of air, 

 the conditions leading to discharge of atmospheric 

 electricity from kite-balloons and cables, and the best 

 shape for parachutes. Few, we believe, will read 

 these pages' without discovering some points of con- 

 tact between aeronautical science and their own 

 particular field of investigation. 



Mention should be made of the verv interesting 

 table of comparative performanres of British aircraft 

 which is included as an appendix. 



Climatic Cycles and Tree-growth. 



PUBLICATION No. 289 of the Carnegie Institu- 

 tion of Washington is devoted to Prof. 

 Douglass's studv of the annual rings of trees in 

 relation to climate and solar activity. When the late 

 Prof. Lowell was seeking an ideal climate for his 

 observatory, with the view of studying the planet 

 Mars, he chose the dry region of Flagstaff, Arizona, 

 on account of its low rainfall and high proportion of 

 clear skies. While Prof. Douglass was at the Lowell 

 Observatory it occurred to him that variations m solar 

 activity might have a measurable effect on tree- 

 NO. 2644, VOL. 105] 



growth, since the latter was probably dependent or» 

 rainfall, and rainfall might very likely be affected by 

 solar activity. He began by studying the yellow pines 

 of those arid regions, arguing that a very dry climate 

 should be the best for such an investigation. He 

 soon found that the intimacy of the connection 

 between the width of the annual tree-rings and the 

 rainfall, when the latter was known, was far closer 

 than he had dared to hope, and he pushed further 

 afield, examining tree specimens and fossils in 

 European collections as well as in other districts of 

 America. 



Considerable labour was involved in the interpreta- 

 tion of the various appearances of the rings, the red 

 tissue that denotes the close of a period of growth. 

 The year starts in the autumn. With normal winter 

 snow and spring and summer rainfall growth con- 

 tinues throughout until the autumn, and a ring of 

 normal width is produced. If winter snow is 

 deficient and spring rain also scanty, a narrow^ ring is 

 produced, closing prematurely without waiting for 

 summer rain. An intermediate condition is shown 

 when winter snow is deficient and the spring drought 

 is not so severe ; red tissue begins to form, but 

 growth starts again, and the result is a double ring 

 for the year. 



The author considers that five trees in a group give 

 a trustworthy result in general, though in a very dry- 

 district like Arizona two might suffice. The only dis- 

 trict where five trees failed to give a satisfactory cross- 

 identification was a rugged region near Christiania, 

 in Norway. 



The Flagstaff record is complete from a.d. 1385, 

 but among the sequoias of California stumps are in 

 existence dating back more than three thousand years. 

 Some of these sequoias grew on hillside slopes, and 

 others in basins where plenty of moisture is found at 

 all times. The latter are unsuitable for investigation, 

 and the author calls them "complacent," as they 

 show practically no variation in the annual growth. 

 The others he calls "sensitive," as they have to 

 depend upon snow melting down the slope and upon 

 rain as it comes, not being ^provided with any storage 

 such as that found in the basins. Some specimens, 

 including the oldest of all, showed signs of a change in 

 environment, "complacent" in later growth but 

 " sensitive " earlier. " Prof . Huntington had previously 

 investigated these sequoias in his search for evidence 

 of climatic change, but his purpose was served with 

 much less detailed measurements, ten-year periods 

 being short enough for his unit of time. His dates 

 agree fairly well with those of the present work. 

 The analysis of the data for periodicities required con- 

 siderable 'accuracy in the method employed, and ulti- 

 mately led to the adoption of the "automatic optical 

 periodograph," of the construction and application of 

 which full details are given. 



Practically all the groups of trees investigated show 

 the sun-spot cycle or its multiples; the solar cycle 

 becomes more certain and accurate as the area of 

 homogeneous region increases or the time of a tree 

 record extends farther back ; this suggests the possi- 

 bility of determining the climatic and vegetational 

 reaction to the solar cvcle in different parts of the 

 world. A most suggestive correlation exists in the 

 dates of maxima and minima found in tree-growth, 

 rainfall, temperature, and solar phenomena, _ pointing 

 to a physica'l connection between solar activity and 

 terrestrial weather. There is a very important point 

 discussed under the title of " Meteorological Districts.;' 

 It is essential to restrict any such district for this 

 purpose to one in which homogeneous weather condi- 

 tions are found. Clearlv, if one set of conditions 

 makes one district wet and a neighbouring district 



