450 



NATURE 



[December 24, 1914 



great service to the reader. The treatment of the 

 design and driving of piles is good and up-to- 

 date, as is also that of bridge piers and abut- 

 ments. 



The book possesses the merit of presenting a 

 fairly complete exposition of a rather difficult 

 subject without unnecessary profusion of detail, 

 and will be welcomed by many students who desire 

 more information regarding foundations than is to 

 be found in the text-books dealing with the theory 

 and design of structures generally. 



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 of Nature. No notice is 

 taken of anonymous cotmnunications ."j 



The Camera in Australia. 



Now that most members of the overseas party of the 

 British Association have, happily, returned safely from 

 the meeting in Australia, it seems opportune to remind 

 members of the scheme for the exchange of photo- 

 graphic prints announced in the Journal (issued in 

 Melbourne on August 12, 1914, p. 2), for which Dr. 

 A. Holt and myself became responsible. The aim of 

 the scheme was to economise our stock of plates and 

 to prevent unnecessary, duplicating of prints. Thus in 

 the advance party in West Australia one member took 

 a photograph of one striking object, a second member 

 of another, on the understanding that all members of 

 the party would be able to obtain, at their own 

 expense, copies of the prints of the photographs, either 

 by an exchange of photographic prints taken by them- 

 selves or by payment of the cost of the print supplied. 

 It was an essential feature of the scheme that the 

 photographers themselves should not suffer financial 

 loss in meeting the requests of members for prints. 



The scheme is sufficiently comprehensive to include 

 not only illustrations of plants, animals, and scenery, 

 but also of any features appealing to members specially 

 interested in any one of the many Sections of the 

 Association's activities. Thus timber felling, aboriginal 

 camps and their life, manufacturing processes, as well 

 as the lighter side of our visit, such as life on board 

 ship and garden-parties, come within the scheme of 

 exchange. In fact, if any member has photographs of 

 interest taken either in Australia or on one of the 

 many routes members followed to and from Australia 

 it is hoped he will be willing to offer prints of the 

 same to others. Though the scheme was intended in 

 the first instance to apply to members of the overseas 

 party and to local members of the Australian meeting, 

 there is nothing to prevent it from developing so that 

 members of the Association who were unable to attend 

 the meeting ma}- have the opportunity of obtaining a 

 set of the photographic prints offered for exchange. 



Will members willing to participate communicate 

 with me, as soon as possible? In each case a list of 

 the prints available, together with the address of the 

 supplier and the cost of the prints, should be given. 

 It would be helpful if a set of the prints could also be 

 sent for inspection and subsequent return. 



From these lists a general list will be prepared and 

 sent to each participator in the scheme. It will prob- 

 ably be an advantage to all concerned if the exchange 

 is worked from one centre. This we shall be willing 

 to undertake in the hope that all will co-operate by 

 promptness of reply in making the task as light as 

 possible. 



It is hoped that the scries of prints will serve not 

 NO. 23=56, VOL. Q4I 



only as a permanent record of our unique and delight- 

 tul experience, but also as illustrative material for 

 teaching, lecture, and museum purposes. Thus mem- 

 bers could at this moment help many deserving chari- 

 ties by giving lectures on Australia with these prints 

 for illustration. T. Johnson. 



Royal College of Science, Dublin. 



Magnetic Disturbances, 1913. 



Dr. W. N. Shaw has asked me to send you an 

 account of an examination, undertaken by his instruc- 

 tions, of the Eskdalemuir magnetograms for 1913. 

 The examination indicates that the disturbances from 

 the level of the quiet day inequality fall into two 

 distinct classes A and B. 



A. — The disturbance was due to a magnetic force 

 which remained in a more or less fixed direction while 

 changing sign in an oscillatory manner. Throughout 

 the year the direction of this force had an azimuth 

 lying within a range of about 60° on either side of 

 the magnetic meridian and an inclination to the hori- 

 zontal lying within the narrow limits 0° and 6°. The 

 slope was upwards towards the more northerly end. 

 An especially clear example occurred on March 23d., 

 i4h. to i8h.' 



Pulsations of periods 2 to 15 minutes fall into this 

 class. A search also brought to light longer periods 

 of 19, 23, and 26 to 30 minutes. Beyond this there 

 are measured periods of 180, 155, 148, 109, 100, 95, 85, 

 80, 80, 78, 74, 66, 60, 38 minutes, but the measure- 

 ments have been uncertain to, say 15 per cent., and 

 should perhaps be taken only to indicate the existence 

 of actual periods near 79 minutes and between 150 and 

 .180 minutes. The crowding together of the shorter 

 periods of 2 to 15 minutes is suggestive of a harmonic 

 series. The longest periods noted were recorded on 

 the afternoons or evenings of June i7d., 2 id., 23d., 

 July od., lod., i2d., i5d., i8d., 25d., August 7d., 9d., 

 I id., 28d. class A appears to resemble the type of 

 disturbance that Birkeland has attributed to a ring- 

 shaped electric current encircling the earth at a great 

 height above the ground in the plane of the magnetic 

 equator. The periods noted above are enormously 

 greater than the time (0-13 second) taken bj' an electro- 

 magnetic wave to travel round the earth. Similarly 

 the wave-length of sodium light is enormously greater 

 than the circumference of the sodium atom. Can 

 there be a similarity of explanation in the two cases? 



B. — The direction of the disturbing magnetic force 

 was not fixed as in class A, but wandered about, 

 usually remaining within 60° of a plane normal to 

 the undisturbed force. The large, slow "bays" near 

 midnight usually fell into this class. For example, 

 the bays on October 7d., oh. to 4h. Sometimes the 

 disturbing force rotated as if it were rigidly attached 

 to an axis nearly coinciding with the direction of the un- 

 disturbed force ; the rotation was clockwise to an 

 observer looking north and down. Class B appears 

 to resemble the types of disturbance which Birkeland 

 has called "polar" and " cyclo-median." 



Class A disturbances sometimes occurred without 

 class B, but class B seldom occurred without A. 



Disturbances of the A class were identified by view- 

 ing the traces of the components laid over one another 

 and pressed against a window-pane. The correspond- 

 ence of the oscillations in the three components deter- 

 mined the matter. 



Further particulars will be published in the British 

 Meteorological and Magnetic Year Book, part iv. 2, 



1913- 



It will be interesting to know whether other 

 observers have found corresponding phenomena in 

 working up records for iqi3. L. F. Richardson. 



The Observatory, Eskdalemuir, Langholm, 

 Dumfries-shire, December 11. 



