lO 



NATURE 



[March 2, 191 1 



Aiagnettsm, vol. xv., p. 231, Table VIII., Nos. 20, 24, 25, 

 28, 30, 31. The letters E (motion of disturbance east- 

 ward or plus motion) and VV (minus or westward motion) 

 jjiven in the last column arc as taken from Table VIIL 

 spoken of ; note how the plus sign is linked each time 

 with E and the minus with the^ W. Surely the most 

 captious critic will hardly contend that this is mere chance. 



As judged by the Venske data, Dr. Krogness's time 

 scalings are in error from — o-5m. to + i-2m., and, on the 

 average, +o-43m., his general tendency being to measure 

 the Potsdam time too low by almost o-5m. It must hence 

 not be surprising that he failed to detect the generally 

 eastward progression in the times between the United 

 States and Potsdam, and was, instead, led to negative 

 results ; the difference of half a minute is precisely on the 

 order of the required quantity. 



Dr. Krogness, in his communication (idem, p. 171), un- 

 wittingly revealed also that the time scalings of his chief 

 — Prof. Birkeland — were likewise untrustworthy. In order 

 to get some definite information regarding the methods 

 employed. Prof. Birkeland was next appealed to directly, 

 but unfortunately in a reply received from him he failed 

 to answer my question. It is recommended that all time 

 data which appear in Prof. Birkeland's vol. i. (Norwegian 

 Aurora Polaris Expedition, 1902-3) be used with extreme 

 care by anyone who wishes to look into the matter of 

 simultaneity of abruptly-beginning disturbances. I am not 

 surprised now that Prof. Birkeland was unable to reach 

 any definite conclusion himself on this interesting and 

 important question, for his data lacked the necessary 

 refinement. 



Since I am on record as believing that no implicit 

 reliance is to be placed upon simply one observatory, no 

 matter how excellent its instrumental equipment and 

 methods may be. Table II. is next given for the fifteen 



Table II. — Greenwich Mean Civil Times of beginning of 

 Disturbances in North America and Europe. 



disturbances spoken of above ; in this all the observatories 

 are embraced the data of which have been received to 

 date, February 10, excepting one the time scalings of which 

 differ occasionally lom. or more from near-by institutions, 

 and are doubtless subject to some error. The " North 

 American group " embraces the six observatories Hono- 

 NO. 2157, VOL. 861 



lulu, Sitka, Baldwin, Agincourt (Canada), Cheltenham, 

 and Porto Rico, the mean gec^raphic position being 

 36-3° N., 1017° W., of Greenwich; the "European 

 group " gives the mean times for the seven observatories 

 Stonyhurst, Greenwich, Uccle, Wilhelmshaven, .Munich, 

 Potsdam, and Katharinenburg, the mean geographic posi- 

 tion being 524° N., 13-6° E., of Greenwich. It will be 

 noticed that Kew is not included, for the simple reason 

 that, although Dr. Chree scaled the required data some 

 months ago, he has not yet published them nor forwarded 

 them to me. The Greenwich data were received the 

 earliest of all, viz. January 23, and those of the distant 

 Observatory of Katharinenburg on February 9. The 

 numbers attached to the various entries in Table II. corre- 

 spond to those in my Table VIII. iTerr. Mag., vol. xv., 



P- ^31)- , ,. . 



The last two columns ascribe the direction of pro- 

 gression of the disturbance according to the sign of the 

 difference E-N, plus meaning east. First the direction is 

 given as derived from the present investigation, which 

 depends upon data over the region from Honolulu, 158° 

 W., to Katharinenburg, 606° E., and next as obtained 

 previously from the five Coast and Geodetic Survey 

 observatories alone (Honolulu, 158° W., to Porto Rico, 

 65-4° W.). Comparing the two columns, it is seen that 

 only in three cases out of fifteen, viz. Nos. 24, 26, and 

 29, do the letters clash ; in other words, in 80 per cent, 

 of the cases the directions, as determined from the limited 

 portion covered by the United States observatories, agree 

 with those now gotten for a considerably larger region. 

 Moreover, Nos. 24 and 29 exhibit the interesting fact that 

 while the disturbance each time progressed eastwardly in 

 Europe just as it did in the United States, yet the mean 

 time of occurrence for each is less in Europe than in North 

 America. These are precisely similar cases to the disturb- 

 ance of May 8, 1902, which seemingly began in the Atlantic 

 and Europe, and then travelled eastward, being felt last 

 in the United States. When the data for the observatories 

 in Asia are available, the actual direction of progression 

 of the two disturbances Nos. 24 and 29 will be known 

 better. This shows, as I have already pointed out, how 

 important it is to know approximately the region where 

 the disturbance originated (cf. Terr. Mag., vol. xv., p. 20). 

 The result from No. 26 is more or less doubtful, evidently 

 the point of beginning being not sufficiently sharp at all 

 stations ; three of the observatories mark their times 

 doubtful, and two omit giving them. 



Both columns unite in showing that the eastwardly pro- 

 gressing disturbances predominated over the westwardly 

 ones in the ratio of about two to one. The average differ- 

 ence E-N, regardless of sign, is o-68m., which was the 

 average time required for a disturbance to pass from the 

 mean position of the North American group to that of the 

 European, or over a great circle distance of 75°. If the 

 disturbance continued to progress at this rate, and were 

 to make a complete circuit of the earth, it would take 

 3-3m., hence on the order of the quantities already 

 announced. The linear velocity here concerned would be 

 about 200 km. per second. 



The available data on the non-simultaneity and pro- 

 gression of abruptly beginning disturbances have now been 

 subjected to so many severe tests that it is difficult to see 

 how anyone with an open mind can any longer doubt that 

 some important discoveries concerning magnetic disturb- 

 ances have been made. I should, indeed, be glad to be 

 informed of any other facts in terrestrial magnetism which 

 have stood as well the tests applied. 



Dr. Chree, unfortunately, in his paper before the British 

 Association last summer, and again before the Physical 

 Society of London on November 11 last (Proceedings, vol. 

 xxiii., part i., December 15, 1910 [49]), devotes chief 

 attention to pointing out difficulties in explanation. He 

 seems more concerned in determining why, according to 

 his ideas, the phenomenon should not be rather in finding 

 out whether it is. One of the chief purposes of my paper 

 was to arouse further investigation on the part of others. 

 Dr. Chree could not have done better than immediately 

 to have published his own data in the same open manner 

 that Mr. Paris had done. Instead, he labours to discredit 

 the Coast and Geodetic Survey obser\-ations, and with- 

 holds his own from public scrutiny. In half the interval 

 of time between the first and second presentation of his 



