March i6, 191 i] 



NATURE 



79 



containing Bombay, Batavia (107° E.), Zikawei (121° E.), 

 and Melbourne (145° E.). Omitting hours, here are the 

 times in minutes assigned for the commencements at the 

 tliree last-mentioned stations : — 



37'0, 397, 87, 487, 527, 427. 207, 44-0, 47, 487, 467, 

 187. 547, 327, 247, 457, 52 7, 



31-3, 32 3, 0-3, 45-3, 46-0, 35-6, 21-3, 38-3, - 1-2, 41-8, 41-0, 

 15"3. 50"3. 273, 20-8, 41-3, 47 4, 



3S-4, 33'4, 51. 500, 55-1, 45-1, 25-1, 45-1, o-i, 55-1, 45-1, 

 151. 501. 35"i, 251, 45 1. 45«. 



The number of 7's in the first and second lines, of 3's 

 in the third and fourth, and I's in the fifth and 

 sixth, tell a tale to anyone who has eyes. It 

 is the treatment of the data, however, to which I 

 would direct attention. Zikawei, though intermediate in 

 longitude, differs usually in the same direction, as regards 

 time of commencement, from Batavia and Melbourne. 

 Its time is earlier than that of Batavia in sixteen cases, 

 and than that of Melbourne in fourteen cases, out of 

 seventeen ; and the mean algebraic difference is no less 

 ihan 5-2 minutes in the one instance and 4-6 in the other. 

 Instead of recognising that data such as these are useless 

 for any purposes of high accuracy, Dr. Bauer gets out 

 means from his two central stations and obtains an 

 average of between three and four minutes for the time 

 of going completely round the earth, a time markedly 

 less than the data employed give between Batavia and 

 Zikawei, stations differing by less than 15° in longitude 

 or 38° in latitude. 



A final criticism I might mention is this : If disturb- 

 ances travel round the earth in the way Dr. Bauer sup- 

 poses, why do not they quite complete the circuit, or 

 even go round several times? In some cases, at least, the 

 amplitudes of commencing movements at stations nearly 

 180° apart are very similar, so that going half-way round 

 can have had but little effect, and movements with a 

 much reduced amplitude would still have been conspicuous. 

 Earthquake tremors, we know, do go round more than 

 once. 



As regards the theory vaguely outlined by Dr. Bauer 

 (pp. 10— 11), I am not surprised by his claim that "the 

 (.'ireful reader will not fail to observe that . . . [it] is 

 considerably different from that which Dr. Chree imputed 

 to me." But unless I had had prophetic powers, how 

 could it have been otherwise? The earlier theory reached 

 or was based on a definite mathematical equation {Terres- 

 trial Magnetistn, June, 1910, p. 123), v — XneD/p, where 

 T is " the velocity of the moving ions . . . n the number 

 of molecules in a c.c. of gas at a pressure p dynes per 

 sq. cm., e the electric charge carried by an ion, D the 

 coefficient of diffusion of an ion through the gas." Of 

 X Dr. Bauer tells us : — " Regarding the variation of X, 

 some preliminary calculations would appear to indicate 

 that the potential gradient of i volt per cm. assumed may 

 be of about the right order of magnitude for the heights 

 concerned " (75 km. is the height finally suggested). My 

 primary difficulties were two. Sir J. J. Thomson, the 

 authority quoted by Dr. Bauer, applies the formula to 

 ions moving in the direction of the field X. Dr. Bauer 

 makes v a horizontal velocity ; but " potential gradient " 

 IS a term usually applied to the earth's vertical field, and 

 100 volts per metre is the value usually ascribed to it, as 

 an average (probably a low one), at ground-level. Poten- 

 tial gradient, in the usual sense of the term, is known 

 from balloon observations to fall to one-tenth of its 

 ground-level value at heights of a few thousand feet, and 

 at 75 km. it is usually supposed to be infinitesimal. If 

 by " potential gradient " Dr. Bauer means a horizontal 

 field, he should say so explicitly, and explain how it is 

 produced and how he reaches his numerical estimate. As 

 regards his concluding remark on the question of theory. 

 If Dr. Chree has something better to offer I shall be 

 glad to know it," I labour under the disadvantage of 

 holding the view — antiquated though it may appear to 

 some of my contemporaries — that before advancing a 

 mathematical theory for any supposed phenomenon, it is 

 desirable to make reasonably sure that the phenomenon 

 ictually exists. 

 If we take Dr. Bauer's latest conclusions respecting the 



NO. 2159, VOL. 86] 



fifteen storms he deals with in Nature, we have nine 

 going east and six west. The mean algebraic difference 

 between the European -and American times of commence- 

 ment, -I- denoting earlier occurrence in America, is only 

 -fo-ii minute. In view of the fact mentioned by Dr. 

 Bauer, that the algebraic mean difference between the times 

 deduced by two skilled observers, Drs. Venske and 

 Krogness, for the commencements of six disturbances at 

 Potsdam — one of the best equipped of stations — was no 

 less than 0-4 minute, I think most physicists of experience 

 will recognise the expediency of awaiting something much 

 more decisive before passing a final judgment. 



March 4. C. Chree. 



Together with Mr. O. Krogness, I am just on the way 

 to Khartoum, in Sudan, in order to carry out some re- 

 searches on the zodiacal light. 



In connection with these investigations, we propose to 

 secure some magnetic records with very sensitive 

 apparatus. Special care will be taken to obtain as accu- 

 rate a time-determination as {X)ssible. 



For one set of observations we shall use an hour-length 

 of 20 mm. ; for another set, with twelve times greater 

 hour-length, records will be obtained between about sh. 

 p.m. and 3h. a.m. Greenwich mean time. 



If at other observatories, especially near the equator, 

 similar rapid records could be secured in the same time- 

 interval, these would, I think, be of value in deciding the 

 question of the simultaneity or non-simultaneity of 

 abruptly-beginning storms. 



Our records are intended to commence on March 20, and 

 will continue for one month. 



Similar records will also be obtained by Prof. S. Saeland 

 in Trondhjem. Kr. Birkeland. 



Berlin, March 3. 



The Centenary of Bunsen's Birth. 



On March 31 it will be one hundred years since Robert 

 William Bunsen was born, and it has been felt that that 

 occasion should not be allowed to pass without his pupils 

 and admirer's in this country giving expression to their 

 veneration of the memory of one of the greatest chemists 

 of our times. A committee has been formed to make the 

 necessary arrangements, and it was intended to celebrate 

 the centenary by a dinner. Unfortunately, the two most 

 distinguished pupils of Bunsen, Sir Henry Roscoe and Sir 

 Edward Thorpe, are at present prevented by indisposition 

 from attending such a celebration. In these circumstances 

 the committee has decided not to proceed with the arrange- 

 ments for a dinner ; but, feeling that the occasion should 

 not be allowed to pass unnoticed, they have resolved to 

 send a signed address to the Heidelberg University from 

 old Heidelberg students in this country, and to place a 

 wreath on the Bunsen monument. May we request those 

 old Heidelberg students who wish to participate in this 

 movement to send their signatures to Prof. H. B. Dixon, 

 of the Manchester University, the chairman of the com- 

 mittee, or to either of the undersigned honorary secre- 

 taries? 



Francis Jones (Manchester Grammar School). 

 J. Grossmann (Plymouth Grove, Manchester). 



Chemical Laboratory, 157 Plymouth Grove, 

 Manchester, March 11. 



Life and Habit. 



Your correspondent " W. II. M." (Nature, March 2, 

 p. 12), who believes that it is necessary for newly hatched 

 chicks to learn to eat by imitation, should see a litter of 

 pigs being lx>rn. Each little pig the moment that he is 

 outside hurries over the sow's hind legs, and, in the 

 second second of his outdoor life, has a teat in his mouth. 

 If the navel-cord has not got clear of his late home, he 

 tugs away at it with all his might. Seeing such a sight, 

 one might suppose that before birth the creature had been 

 eagerlv looking forward to his first breakfast. Or did the 

 splendid prospect flash into his mind only as he found his 

 feet? Francis Ram. 



54 St. John's Road, N., March 13. 



