October 13, 1910J 



NATURE 



463 



vented bv illness or other causes from aitending". 

 Among them were Sir David Gill, Dr. Lockyer, Profs. 

 Righi and N'ioUe. To the great regret of everyone 

 present, Prof. Hale was prevented by bad health, 

 brought on through overwork, from taking part in 

 the discussions. Together with Mrs. Hale, he re- 

 ceived his guests at a garden-party at their home in 

 Pasadena, and was able to come up to the observa- 

 tory on the first day of the meeting, but on the advice 

 of his doctor he returned to Pasadena, after deliver- 

 ing a short address on the general work of the con- 

 ference. 



.As regards the results of the meeting, the first 

 place must be given to the extremely satisfactory 

 report of the committee on the determination of 

 standard wave-lengths. The requirements of modern 

 spectroscopic research having rendered all previous 

 measurements obsolete, even for purposes which oni 

 require relative values, the Solar I'nion set itself the 

 task of preparing new tables. The direct comparison 

 between the wave-lengths of the red cadmium line 

 with the standard metre carried out bv Fabry and 

 Perot gave a result practicallv identical with that of 

 Michelson, so that already three years ago its 

 numerical value could be definitely adopted. Taking 

 this line to be the primary standard, a sufficient 

 number of iron lines had next to be compared with 

 i'c, so that thev might serve in subsequent work as 

 secondarv standards, with an accuracy hardly, if at 

 all, inferior to that of the primary. This work was 

 undertaken independentlv in three different labora- 

 tories bv Fabrv and Buisson, at Marseilles, by Ever- 

 sheim under Kavser at Bonn, and bv Pfungst under 

 .\mes at Baltimore. The numbers obtained agree so 

 well that we are nov,- already in possession of a large 

 number of lines with accurately known wave-lengths. 

 How accurately? L'sin."- the Angstrom (lo-* cms.) 

 as unit, the average differences of the three inde- 

 pendent determinations onlv amount to about three or 

 four in the third decimal place, which means less 

 than one part in a million. The few cases where 

 the differences are somewhat greater are easilv ex- 

 plained by a deficiencv in the homogeneitv of the 

 lines, except in a small region in the orange. 



The secondary standards are now sufficientlv close 

 together to serve as fixed points for interpolations, 

 when gratings are used, and it is intended to pro- 

 ceed immediatelv with the further determination of 

 tertiary standards so near to each other, that even 

 with a prismatic dispersion every observer will have 

 at his command a system of lines on which he can 

 depend entirelv for comparison or interpolation. In 

 the orange region referred to, some barium lines will 

 have to be added, and the total length of spectrum 

 dealt with, which extends from X .J282 to X 6494., will 

 before long be substantially increased on the red side. 

 In order to avoid confusion between the new and old 

 determinations, the now adopted unit will be known 

 as the "international .Angstrom" (I. .A.). If the Solar 

 Union had done nothing else than this work on 

 wave-lengths, it would have justified its existence. 



We next note the report of the committee on the 

 investigation of sun-spot spectra, which was presented 

 by Prof. Fowler. Its work is sufficientlv indicated 

 bv the following recommendations, which were 

 adopted by the meeting : — 



(i) Thai, notwithstanding the progress of photo- 

 graphic work, visual observations of spot spectra 

 should be continued, and that the committee should 

 be re-appointed to continue the organisation of this 

 work. 



(2) That in view of our increased knowledge of 

 spot spectra, the committee should be authorised to 

 prepare and circulate a revised and extended scheme 

 of visual observations. 



NO. 2137, VOL. 84] 



(^) That it is desirable that, for the use of visual 

 observers, the separate sections of the new photo- 

 graphic map of the sun-spot spectrum should not ex- 

 ceed 60 centimetres in length, and should be on a 

 scale of 5 mm. to the .Angstrom. 



Another committee dealt with spectroheliograph 

 work, and here also we may confine ourselves to quot- 

 ing the more important resolutions : — ■ 



(i) That daily photographs of the calcium flocculi 

 be continued by the co-operating observatories. 



(2) That provision be made, if possible, for the 

 measurement of the photographs. 



(3) That the desirability of utilising large spectro- 

 heliographs of high dispersion for the study of the 

 upper lavers of the solar atmosphere is recognised by 

 the committee. 



A report on the spectroheliograph work carried on 

 at South Kensington was sent in by Sir Norman 

 Lockver, and will be printed in the transactions of 

 the union, as also a discussion of solar phenomena 

 as revealed bv the spectroheliograph, which was pre- 

 sented by M. Deslandres. 



An important, but from the nature of things some- 

 what slowlv progressing, committee deals with the 

 studv of solar radiation. Its work has been seriously 

 retarded bv the lamented death of Knut Angstrom, 

 whose pvriieliometer had been adopted by the union 

 as standard instrument, and who had undertaken per- 

 sonallv to standardise all pyrheliometers sent out 

 from Upsala. Latterlv serious defects in the con- 

 stancy of the indications of the instrument have 

 shown themselves, and unless a readv means is found 

 to keep an accurate log of their changes by frequent 

 comparison with some standard radiator, the union 

 will be forced to modify its previous decision. Mr. 

 Abbott presented the report of the committee, and 

 gave an account of his own important work on solar 

 radiations, which has revealed some fluctuations in 

 the amount of heat and light which enters our atmo- 

 sphere. . These, fluctuations, which frequently amount 

 to ■; or 6 per cent. ,.mav still be due to uncorrected 

 influences of atmospheric absorption, and Mr. .Abbott 

 laid stress on the inlportance of establishing an inde- 

 pendent station in a locality where the atmospheric 

 conditions are favourable, so that simultaneous 

 observations can be carried out, at least in two places, 

 and atmospheric inequalities still further eliminated. 



It remains to record an important alteration in 

 the constitution of the union, which has decided to 

 extend its scope, and include astrophvsics in the range 

 of its activitv. In voting for the change, the mem- 

 bers of the union were fully aware of the itiiportance 

 of their decision. It was pointed out by several 

 speakers that the union exposed itself to the danger 

 of undertaking more than could be managed, and 

 that before long the primary object of the union 

 might be swamped bv the additional problems now 

 introduced. But, on the other hand, everybody re- 

 cognised that the distinction between the sun and a 

 star was an artificial and accidental one, and that 

 the studv of one was a necessary complement to the 

 studv of the other. The danger of being over- 

 whelmed bv the additional subjects is not great, be- 

 cause onlv a few well-defined portions of astrophysics 

 are adapted for investigation by international co- 

 ooeration. .At the conclusion of an interesting dis- 

 cussion, the vote went unanimouslv in favour of the 

 change.. .A beginning of the new order of things was 

 made at once, and a committee was appointed, with 

 Prof. E. Pickering as chairman, to discuss the pos- 

 sibilitv of coming to an agreement on the classifica- 

 tion of stellar spectra. 



The next meeting of the union will be held at Bonn 

 in the vear 1913. 



.Arthur Schuster. 



