May 26, 192 1] 



NATURE 



399 



The Recent Magnetic and Electrical Disturbances. 



By Dr. C. Chree, F.R.S. 



THE recent magnetic and electrical disturb- 

 ances have been remarkable for both their 

 intensity and their persistence. Magnetic dis- 

 turbance went on without any considerable inter- 

 lude from shortly after I3h. (G.M.T.) on May 13 

 to 4h. or 5h. of May 17. This was followed by 

 notable disturbances on May 19 and following 

 days. There was, however, a distinctly quieter 

 interval between May 17 and 19. Thus the storm 

 was really less persistent than one presenting very 

 similar features which began late on November 11, 

 1882, and continued practically without a break 

 for nine or ten days. 



As regards aurora, much depends on the season 

 of the year, the age of the moon, and the amount 

 of cloud. In the North of Scotland, the principal 

 auroral region of the United Kingdom, twilight 

 lasts so long in May that the chance of aurora 

 being visible is but small. During the recent 

 magnetic storm, aurora, if not generally brilliant, 

 has been seen in a number of places. At Cam- 

 bridge, aurora was seen to rise as high as the 

 zenith on the night of May 13, and in the early 

 morning of May 15 aurora was observed with a 

 bright red colour. Aurora was also reported from 

 London and other stations in southern England, 

 where it is a rare event even at the equinoxes. 

 Large earth-currents have been observed in the 

 Post Office telegraph system at stations in 

 England, Scotland, and Ireland. 



The magnetic disturbances recorded at all the 

 magnetic observatories have been of a quite ex- 

 ceptional nature. They reached a climax on the 

 night of May 14-15. Almost all large magnetic 

 storms show shorter-period oscillations superposed 

 on changes having a more or less persistent direc- 

 tion for a considerable time. But the extent to 

 which short-period oscillations prevail varies much 

 in different storms. Also in many cases, while 

 the disturbance of the horizontal components is 

 considerable, the vertical force (V) shows little 

 disturbance, and rapid oscillations of any size In 

 that element are very rare. During the recent 



disturbances the persistence and size of the short- 

 period oscillations were remarkable, and during 

 the night of May 14-15 this characteristic was 

 shared by V to a quite exceptional extent. The 

 magnetic storm of November, 1882, already re- 

 ferred to, also showed this phenomenon, so that, 

 though rare, it is not absolutely unique. The year 

 1882, it may be noted, like 1921, was not char- 

 acterised as a whole by abnormal sun-spot develop- 

 ment. 



The storm has received unusual attention in 

 the newspapers. The writer of a leading article 

 on the subject in the Times of May 19 has re- 

 ferred to the difficulty of providing the large store 

 of energy required, seeing no alternative to the 

 acceptance of the estimate made many years ago 

 by Lord Kelvin other than the giving up of the 

 principle of the conservation of energy. As the 

 storm considered by Lord Kelvin was very trifling 

 compared with the recent one, the conservation 

 of energy may appear in a hopeless case. It may 

 thus comfort the general reader to know that a 

 recent estimate by Prof. S. Chapman gives a 

 result which is nearly one million-million-million 

 times less than Lord Kelvin's. When Lord Kelvin 

 made his estimate his position resembled that of 

 an eighteenth-century engineer consulted as to 

 the possibility of warming London by burning coal 

 in the Midlands. The better the engineer of that 

 epoch, the deeper the pessimism to be expected. 

 But the modern engineer, familiar with high- 

 tension electrical transmission, whatever he might 

 think of the scheme as a financial proposition, 

 would not consider its realisation fatal to the 

 conservation >of energy. 



If, as some modern theorists have suggested, 

 atmospheric electric potential at the earth's 

 surface should show some response to magnetic 

 disturbance, the morning of May 15 was the time 

 when the phenomenon should have declared Itself. 

 Unfortunately, some rain fell that morning in 

 London, and a decisive answer to the question 

 must be sought elsewhere. 



The Recent Large Sun-spot Group. 

 By H. W. Newton, The Royal Observatory, Greenwich. 



THE large sun-spot which appeared on May 8 

 is remarkable in several respects. The 

 sun-spot cycle reached its maximum in 1917, and 

 the occurrence of a large group some four years 

 later, though by no means unique, is a matter of 

 interest apart from its association with an Intense 

 magnetic storm. The spot group has been photo- 

 graphed daily at Greenwich, and reproductions of 

 some of the photographs are given. Fig. i shows 

 the disc of the sun on May 13, on which day the 

 magnetic storm commenced. Fig. 2 Illustrates 



NO. 2691, VOL. 107] 



the group in detail and the considerable changes 

 taking place in a few days. The most Interesting 

 features of the group are (a) its position exactly 

 on the sun's equator; (b) its abnormal develop- 

 ment; (c) its position at the time of the magnetic 

 storm. 



(a) It Is a well-established fact that the change 

 in latitude of the sun-spots Is cyclical in the same 

 eleven-year period as their frequency. Soon after 

 the commencement of a new cycle, spots appear 

 mainly about latitude 25° north and south of 



