38 



NA TURE 



[July S, 1909 



smaller size to the water, would have the effect of 

 increasing the average weight of the stock of fish in 

 three j'ears' time, and would, we think, have pre- 

 vented the red flesh of some trout being attributed to 

 richer feeding rather than to a differently constituted 

 menu. We think, too, that the theory set forth to 

 account for the absence of a run of salmon in some 

 rivers of the east of Scotland in May, June, and July 

 is somewhat strange, and cannot be maintained in the 

 light of our present knowledge of the salmon's life- 

 history. 



There are throughout the book numerous practical 

 hints of value upon such subjects as flies and baits, 

 and as to the time and place for fishing under various 

 conditions of water and weather ; in the last chapter 

 there is also a most thrilling tale of a riverside adven- 

 ture. The illustrations, reproduced from photographs, 

 are excellent, but are almost invariably separated by 

 many pages from the corresponding text, and there is 

 a good index. L. W. B. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part 0/ Nature. 

 No notice is taken of anonymous communications.] 



A New Departure in Seismology. 



On the pliotogriiphic records obt.TJned from British 

 Association types of seismograph it has been noticed that 

 when the films have been moving slowly (60 mm. per 

 hour) there have been slight thickenings in the trace, while 

 if the recording surface has been moving quickly (240 mm. 

 per hour) the line which ought to be straight is slightly 

 wavy. These irregularities, which have hitherto received 

 but slight attention, are so small that they may be easily 

 overlooked. When the thickenings were first observed it 

 was supposed that their existence was due to a flickering 

 at the source of light or to some irregularity in the move- 

 ment of the record-receiving surface. When, however, it 

 was observed that these markings frequently occurred at 

 the same time at different stations, as, for example, at 

 Shide and Bidston, the conclusion was that they were due 

 to movements of the ground, and might be the surviving 

 phases of large movements with origins at a distance. 



A very good illustration of this is given by comparison of 

 the times of occurrence of the after-shocks which followed 

 the earthquake of January 14, 1907, in Jamaica, with the 

 times at which suspicious irregularities were found on the 

 seismographic traces at Shide and Bidston. Between 

 January 14 and July 5, 14S shocks were noted in Jamaica. 

 Forty-three minutes after the occurrence of fifty-one of 

 these shocks irregularities were found on the films at the 

 stations mentioned. .As forty-three minutes is the time we 

 should e.Npect a " surface " wave to travel sixty-seven 

 degrees, or from Jamaica to England, the inference is that 

 the slight irregularities represent movements which had 

 their origin in Jamaica. Corresponding markings, with 

 the exception of one at Gottingen on July 5, do no^ appear' 

 in the registers from European stations, which are not 

 more than six or seven degrees farther from Jamaica than 

 Britain. 



Another instance of the recording of after-shocks are the 

 markings seen on seismograms after the disaster which, on 

 December 28, 1908, ruined Messina and Reggio. Between 

 December 29 and January 30 at Mileto, forty miles from 

 Messina, 225 shocks were noted. Eight of these reached 

 the Isle of VVight, while on January i and 13 at Gottingen, 

 Hamburg, and Laibach, only tw^o were noted. The reason 

 that so small a number travelled a considerable distance 

 indicates that the originating impulses were w^eak. That a 

 larger number should be recorded in Britain than at com- 

 paratively near stations is not so clear. 



With smoked paper recording surfaces, whether the 

 multiplication of recording levers be 10 or 200, a certain 

 slackness in joints and elasticity of pointers prevents any 

 record of motion being obtained until a certain amplitude 

 of ground motion has been reached. With photographic 

 NO. 2071, VOL. 81] 



recording apparatus where a light source is far from a 

 recording surface, a thick line may obscure any minute 

 movement. These instruments arc therefore unsuitable as 

 recorders of very small movements. This, at any rate, has 

 been my experience. 



The British .Association type of instrument, when 

 properly adjusted and installed, does, however, pick up 

 these neglected movements — a result which is shown very 

 clearly in the registers for this year. 



It seems to me that beneath observatories all over the 

 world earth-messages may be passing every few minutes, 

 but these are not recognised because instruments generally 

 in use are not capable of recording the same. To investi- 

 gate this possible new departure in seismology, old types 

 of instruments will have to be improved or new ones 

 adopted. John Milne. 



.Shide, Isle of Wight, July 2. 



Tables of bessel Functions. 



A COMMITTEE of Section .\ of the British .Association for 

 the .Advancement of Science, appointed to undertake the 

 further tabulation of Bessel functions, is at present con- 

 sidering the advisability of unifying and completing the 

 existing tables with the view of the publication of a 

 complete table of Bessel functions. 



The committee would be glad of information as to exist- 

 ing tables of Bessel and Neumann functions with a real 

 or complex argument, in addition to the following, of 

 which the members are already aware : — 



(i) Meissel's Tables (reprinted in Gray and Mathews' 

 treatise on Bessel functions) giving J„(.v) and J,(.v) from 

 x = o to a = i.v5 at intervals of o-oi [12 places]; also a 

 table of the first 50 roots of the equation J,(a) = o to 

 i6 places. 



(2) British Association Tables (1889, 1893, 1896 Reports) 

 giving I„(.v) and I,(i-) from x = o to a; = 5i at intervals of 



0001 [9 places]; also I„(a:) to I./a:) from x = o to .\- = 6o 

 at intervals of o 2 [11 and 12 significant figures]; also a 

 table of Jo(.vv'') from x = o to x = 6 at intervals of 02 

 [9 places]. (Part of these tables are reprinted in Gray 

 and Mathews.) 



(3) Tables of J„(.v) in Gray and Mathews from n = o to 

 » = 6o and from x = o to a: = 24 at intervals of unity 

 [18 places]. 



(4) B. A. Smith's Tables giving Y„(.r), -Y,(.v), 

 (log2-7)J.(-v)-Y„(.v)_ and (log 2-7)J,(.x)- Y,(a:), from 

 x = o to .v=ioo at intervals of o-oi and from a:=i-i to 

 .v=io-2 at intervals of o-i (4 places: error not exceeding 



2 in the last place]. (Messenger of Maths., vol. xxvi., 

 1897, and Phil. .Mag., vol. .xlv., iSgS.) 



(5) .ildis' Tables of !,(«), I,(.'v), K„{x). K,{x) fronj 

 * = o to a:=ii at intervals of o-i [16 places]. (Roy. Soc. 

 Proc, 1S96 and 1899.) 



(6) /. G. Isherwood's Tables of K„{x) to K,„(a;) from 

 x = o to .•v = 5 at intervals of 02 [5 significant figures]. 

 (Manchester Lit. and Phil. Soc, vol. xlviii., 1904.) 



The committee will be grateful to be allowed, through 

 the medium of N.iture, to invite any readers who ace 

 aware of the existence of tables of Bessel functions other;" 

 than the above to make known this fact. 



Communications should be addressed to the secretary of! 

 the committee, Dr. L. N. G. Filon, University College,! 

 Gower Street, W.C. M. J. M. Hill. 



University College, Gower Street, W.C. 



Baskets used in Repelling Demons. 



In the issue of Nature published on May 27 Mr.^ 

 Kumagusu Minakata inquires regarding the use of baskets 

 in repelling demons in countries other than Japan. In 

 Calcutta, and I believe in other parts of India, it isj 

 customary when a new building is being erected to set up 

 on the highest part of the scaffolding a pole, to the top 

 of which a round basket and a scavenger's broom are 

 attached. The basket and broom are apparently recognised'^ 

 as emblems of the low-caste " sweeper," and therefore as 

 being disgusting objects. They are supposed to ward off 

 ill-luck from the building. Their use in this instance may 

 thus be compared to the use in many countries of obscene 

 objects or gestures as a protection against malicious spirits 

 or the evil eye. N. Annandale. 



Indian Museum, Calcutta, June 13. 



