44 



NATURE 



[January 12, 1922 



life." It will not become anything of the sort of its 

 own volition, as scientific workers are not usually 

 interested in broad problems outside their own par- 

 ticular fields, and those who have to be forced into 

 the work are best out of it. 



Functioning best begins with a real task, however 

 difficult, before the particular community, preferably 

 the first task which involves large sums of money, 

 large expenditure of time and of energy, and con- 

 siderable risk to human life. These tasks exist in 

 bewildering profusion. The knowledge, without which 

 they cannot even be stated correctly, exists also, and 

 the' prize of efficient performance cannot be won apart 

 from its application. With human contact and the 

 common sense of an adaptable race, tasks and know- 

 ledge can approximate each to each, and the first step 

 in the unity of purpose which science can best bring 

 to national' life may be taken to-day in any city of 

 the country, ' J- J- Robinson 



(Secretary of the Parliamentary Committee 

 of the British Science Guild). 



6 John Street, Adelphi. London, W.C.2, 

 January g. 



Terrestrial Magnetic Disturbances and Sun-spots. 



May I add a few remarks on Mr. Evershed's in- 

 teresting letter on this topic (Nature, December 29, 

 p. 566), and supplementary also to my former letter 

 (Nature, October 27, p. 272). The protracted mag- 

 netic storm of May 12-21, 192 1, after a lull on 

 May 18, resumed an active phase on May 19-21. In 

 my former letter I traced a sequence of magnetic 

 disturbances, in connection with that of May 21, 

 which extended to October 5. I may now add that 

 the sequence has persisted until December 24, that is 

 for 217 days, embracing eight synodical rotations of 

 the sun, with a mean period of 27- 13 days. The corre- 

 sponding mean sidereal period would be 2525 days, or 

 14-26° per day. This is Carrington's rotation period for 

 latitudes 10° to 15°, and agrees closely with the 

 sidereal period found by Mr. Evershed for the main 

 series of disturbances from March 22 to September 29, 

 1921. 



With regard to the series ot disturbances from 

 January i to November 21, 1920, which was also 

 recorded at this observatory, Mr. Evershed deduces 

 the equivalent solar period as 2522 days, which is 

 Carrington's value for spots about latitude ±10°. He 

 reniarks : "The slight difference of period compared 

 with that obtained from the 192 1 series does not 

 make the evidence for these sequences less con- 

 vincing." To my mind, in this particular case at 

 least, it makes the evidence more convincing, because 

 the mean latitude of the sun-spot group observed 

 from December, 1920, to May, 192 1, was about —6°, 

 and, in fact, in the January appearance extended from 

 0° to —12° in latitude. In the case of the 1921 group. 

 May 9-17, the mean heliographic latiiude was +08°, 

 but it extended north of the equator at least 5° in 

 latitude, sufficiently in accord with a sj-nodical rota- 

 tion period of 27-13 days. A. L. Cortie. 



Stonvhurst College Observatory, January 2. 



Reform of the Calendar: Mean Value of the Year. 



I see there is to be a meeting at Rome in 1922 to 

 consider questions concerning the calendar. I should 

 like to direct attention to the fact, apparently little 

 known — I, at least, have never seen it in any book — 

 that if we make the year equal to 365 218/900 days 

 we get a very good approximation, and one which" 

 can be applied by omitting leap-years at certain com- 

 plete centuries, something like what is being done 

 under the present Gregorian rule. If we say that " a 

 NO. 2724, VOL. 109] 



century-year shall be a leap-year only if it gives a 

 remainder of 2 or 7 when divided by 9," we have a 

 rule which is much more approximate than the Gre- 

 gorian rule, and one Which has been followed de facta 

 since 1582 (year of the Gregorian reform). The new 

 rule would ' not differ in its application from the 

 Ciregorian rule before the year 2400. The Gregorian 

 year, 365 97/400 days, differs from the true tropical 

 year by 26 seconds •,' if the above modified rule were 

 introduced the difference would be reduced to 

 2 seconds. 



The "Encyclopaedia Britannica " in the article 

 "Calendar" mentions the value 365 31/128, which, 

 no doubt, is very approximate (difference from true 

 year i second), but depends on the awkward cycle 

 of 128 years ; and, besides, its application would mean 

 a new break in the way of introducing, or rather sup- 

 pressing, leap-years. Arthur Rose-Innes. 



Yokohama, November 27. 



Units in Aeronautics. 



Please allow me to protest against Mr. A. R. 

 Low's attack in Nature of January 5, p. 12, on the 

 "slug," which was not introduced by Prof. Bairstow, 

 but probably by Prof. Fleeming Jenkin about thirty 

 years ago. " The slug does not lead to any evasion 

 of Newton's laws any more than the poundal which 

 was introduced by Prof. James Thomson. All such 

 terms are useful so long as they are precisely defined 

 and correctly understood ; in recent years a distin- 

 guished German mathematician has been striving 

 to introduce Prof. Thomson's "radian" in place of 

 " Einheitskreisbogenlange." 



The contempt common amongst chemists and 

 physicists towards so-called "engineers' units " is 

 without justification. The chemist or physicist derives 

 his unit of force from a definition of mass and ac- 

 celeration, whereas the engineer derives his unit of 

 mass from a defi-nition of force and acceleration. 

 The engineer's reason is that his problems come to 

 him in terms of forces, and he wants his solution in 

 the same units. Engineers on the Continent use the 

 kilogram as the unit of force, and derive a metric 

 slug in terms of the metre and second. 



The ideologist is fond of so-called "absolute" 

 units, but the physical meaning of Newton's or other 

 laws is often made more clear when units are chosen 

 conveniently. An ordinary man cannot realise a force 

 of a dyne, though an insect might collapse under it ; 

 and while an astronomer measures distances in light- 

 years, the peasant uses hours of walking and the 

 spectroscopist /x. It is unlikely that the British or 

 foreign working-man will ever ask for his beer in 

 cubic centimetres : the unit is inconveniently small. 



Chiswick, January q. H. S. Rowell. 



A Curious Physiological Phenomenon. 



The phenomenon to which attention is directed by 

 Mr. F. C. Dnnnatt in Nature of December 22, p. 529, 

 is an exceedingly interesting one, and may be the 

 explanation of what occurs in "table turning" and 

 "hat turning." Many have, no doubt, seen the hat, 

 upon which many finj^ers are resting, move in a very 

 peculiar manner^ and it is difficult to believe that 

 those who are engaged in the exhibition are not telling 

 the truth when they declare that they are not aware 

 that they are the cause of the movements. .\n essen- 

 tial elernent of the game is that the weight of the 

 arms should be carried by the muscles, and it is 

 interesting to learn that such strained conditions lead 

 to involuntary muscular movements. 



R. M. Deeley. 



Tintagil, Kew Gardens Road, Kew, Surrey, 

 December 24. 



