January 5, 191 i] 



NATURE 



307 



Mav 8, 1902, was a two-fold one : first, the stronger, a 

 -et of electric currents which, if negative, circulate in the 

 upper regions around the earth eastwardly (anti-clockwise) 

 if one were looking down on the North Pole, and secondly, 

 a weaker system, imbedded within the earth, possessing 

 the characteristics of directly induced magnetism. It is a 

 matter of interest that the harmonic analysis prescribes 

 the same direction of progression around the earth for the 

 upper negative electric currents as has been revealed by 

 the generally eastwardly progression of the times of 

 beginning ; and it is natural, then, to inquire whether 

 these overhead negative currents consist of negative ions 

 moving ai the rate of lOO to 200 kilometres per second, the 

 resulting effect of which on our magnetic needles is merely 

 an exhibition of the Rowland effect on a scale far 

 transcending any laboratory experiment. 



We have found that the speed of these negative charges 

 nust be on the order of about I'soo that of kathode rays. 

 My provisional calculation showed that if we are dealing 

 l^.ere with moving ionic charges, then at the height of 

 ibout 75 kilometres the rarefaction of the air and the 

 aher necessary conditions, so far as can be judged from 

 -urface experiments, would be such as give a velocity of 

 ihe order required to satisfy the apparently slow propaga- 

 tion of magnetic effects over the earth. The lower the 

 urreni gets down the slower the speed, and, if other 

 things are equal, the greater the effect. Whether this is 

 v\ accordance with actual observation is at present under- 

 j;oing an examination. 



Now let us look briefly at the matter in another way. 

 suppose a negative ion is set in motion at a given alti- 

 tude and in an easterly direction ; the deflecting effect of 

 :he earth's magnetic field on the eastwardly moving 

 negative charge is to bring it down closer to the earth. 

 But, as we have seen, the ionic velocity decreases with 

 lecrease of altitude, and hence the magnetic effect pro- 

 luced by the moving charge on a needle at the surface 

 would begin later and later as the charge travelled east- 

 ward. If, on the other hand, the negative charge started 

 westward around our planet, then the deflecting effect of 

 tile earth's magnetic field would be to make the charge 

 move higher and higher or faster and faster. We might 

 lius possibly have the following state of things : due to 

 ~ome cause, electric charges are set in motion in every 

 direction from a given point overhead. Those with an 

 ''-asterly component of motion would have their velocities 

 checked in the manner just described, whereas those having 

 a westerly component would have them increased, so that 

 for two stations, one east and one west, the magnetic 

 effect might be recorded later at the east station than at 

 the west one — as we have actually found to have been the 

 case in the vast majority of the thirty-eight cases above 

 treated. 



Dr. Krogness next attempts to break down the testi- 

 mony regarding non-simultaneity of commencements of 

 sudden storms furnished by Mr. Paris {loc. cit., pp. 93- 

 105). Dr. Krogness notwithstanding. Mr. Paris does 

 make a statement (p. 98) as to his method of time scalings 

 and the various matters involved to secure the desired 

 accuracy. It is the custom in the Coast and Geodetic 

 Survey to take into account every possible source of error, 

 and as the result Mr. Paris says : — " It would thus appear 

 that with especial care the times could be scaled from the 

 magnetic records within one-half minute in any individual 

 case."* He furthermore states (p. 105): — "In closing, it 

 seems proper to state that the scaling of the times of the 

 "beginnings of sudden impulses is not so difficult a matter 

 as it is to ascertain the exact correspondences in the curves 

 at different stations, for the form of the photographic 

 record of the starting impulse is not always exactlv 

 the same at different places ; that is to say, the fixing of 

 the exact point of the beginning of the disturbance is 

 sometimes more difficult than the reading of the time after 

 the point is decided upon. This difficulty arises chieflv 

 from the fact that the magnetic traces, except in tropical 

 latitudes, are much of the time not smooth curves." 



l_ In the December, 1910, issue (Soc. «7.) Mr. Farts has two communications 

 which will give further eWdence on the matter of accuracy of his time 

 scalings to which Dr. Krogness may be referred. 



NO. 2149, VOL. 85] 



This matter of being sure of having precisely the same 

 perturbation for all stations is one apparently insufficiently 

 considered by Dr. Krogness. Por example, he questions 

 our time of beginning in the H disturbance for the storm 

 of May 8, 1902, as recorded at Potsdam. I gave i2h. om., 

 and he gets uh. 58m. ; I have had our scalings gone over 

 once more, and have this to say : unless the Potsdam 

 Observatory has revised the data furnished us (copy of 

 magnetogram and accompanying time data), the time 

 given by Dr. Krogness is wrong, and i2h. om. is correct. 

 If our Potsdam data are correct, then Dr. Krogness has 

 either made an error somewhere, e.g. may not have con- 

 sidered the fact that the middle of the hour breaks in the 

 Potsdam curves is for local mean time, not for middle 

 European time, or he has taken a small preliminary tremor 

 observed at some of the stations, but of a different 

 character than the particular perturbation considered. He 

 should also remember we had before us the curves of 

 twenty-five observatories, with the aid of which the 

 identical characteristic p>oint could be determined upon for 

 each, so far as that is possible. 



Another fundamental fact in terrestrial magnetism of 

 which Dr. Krogness is not aware is this : the existence 

 or non-existence of a terrestrial magnetic phenomenon 

 cannot be proved by one magnetic observator}, no matter 

 how excellent and suf>erior its equipment may be — not 

 even the whole European group, consisting of about twenty 

 magnetic observatories, would in certain instances suffice. 

 Since the publication of the papers criticised by Dr. 

 Krogness, a prediction which I made has been found true. 

 On p. 25, loc. cit., I say : — 



" In fact, I confidently expect, as soon as a complete 

 analysis has been made of magnetic disturbances covering 

 the greater portion of the earth, it will be found that the 

 disturbance field, in general, presents all the same 

 characteristics of the terrestrial, primary one — the disturb- 

 ances will themselves reveal effects from terrestrial, con- 

 tinental, regional, and even local causes (earth currents, 

 for example, whose path and intensity depend upon local 

 character of soil, &c.)." 



Mr. Paris has brought together for the March, 191 1, 

 issue (loc. cit.), the data from observatories all over the 

 globe with respect to some peculiar magnetic disturbances 

 which occurred between December 29 and 31, 1908. With 

 his permission I will anticipate by saying that these dis- 

 turbances, of which there were eight cases, occurred each 

 time over restricted regions of the globe — e.g. in the United 

 States and not in Europe, or vice versa, &c. The interval 

 between the occurrence of the disturbance in the United 

 States and Asia, or Asia and Europe, was not a matter 

 of a few minutes, but a matter of many hours ! Though 

 this disturbance — whenever it occurred — never lasted much 

 more than half an hour, and was during an otherwise 

 magnetically calm day, nevertheless a number of observa- 

 tory directors are on record as having recognised it and 

 having characterised the day as disturbed (class 1). The 

 interesting point is, however, that they did not all get it 

 at the same absolute time, but at times differing by many 

 hours ! A discussion will be given in the March issue 

 {loc. cit.). 



Hence, by attempting to disprove a fact based on such 

 extensive data as referred to above, with the aid of data 

 at one observatory — Potsdam — Dr. Krogness has simply 

 shown that he is unfamiliar with a fundamental fact 

 regarding the distribution of magnetic phenomena. Everv 

 magnetic phenomenon known to me partakes of a most 

 complex character, and to get a general result of value it 

 is necessary to base an investigation, not simply upon one 

 station or one part of the earth, but on as great a portion 

 of the earth as possible — the greater the better. 



Dr. Krogness next reverts to the disturbance of January 

 26, 1903, the times for which were scaled by Prof. Birke- 

 land. He exhibits a rather interesting method of dis- 

 crimination between the various stations, and appears to 

 have overlooked where his own figures lead. He rejects 

 in toto the three Coast and Geodetic Survey magnetic 

 observatories, Honolulu, Baldwin, and Cheltenham — the 

 latter two probably because Prof. Birkeland had found the 

 identification of the point of beginning of the disturbance 



