414 



NATURE 



[August 28, 1890 



Elementary Arithmetic. By C. Pendlebury, M.A., 

 F.R.A.S., and W. S. Beard, F.R.G.S. (London: 

 George Bell and Sons, 1890.) 

 In a book on elementary arithmetic it is necessary that 

 there should be throughout a good and well graduated 

 series of examples. The authors of the present volume 

 have got together a large number of examples and problems 

 for written work, and in addition they have arranged 

 numerous sets for use in oral teaching form, a very 

 important feature in an elementary work of this kind. 

 The explanatory matter is written in intelligible and 

 simple language, and great attention has been paid to 

 the treatment of the money rules and the more impor- 

 tant weights and measures. 



This book is intended to serve as an introduction to 

 the one on " Arithmetic for Schools," and the examples 

 have been arranged so that they are all different from 

 those given in the advanced work. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed 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 communications. ] 



British Association Procedure. 



It has been to me a matter of surprise that a letter by Prof. 

 O. Lodge published in these columns on October 17, 1889, did 

 not elicit other similar communications, as the views he enun- 

 ciated are undoubtedly those of a not inconsiderable number of 

 active members of the British Association. Prof. Lodge pointed 

 out that the British Association week undoes the benefit of the 

 previous holiday, mainly because the conditions under which the 

 work of the Sections is carried on are prejudicial to health. 

 This I know from considerable personal experience to be the 

 case ; and in this and previous years I have had the remark 

 addressed to me : " Surely you are not going to that British 

 Association meeting to make yourself ill again." 



Prof. Lodge suggested that the Sections should sit from 10 

 a.m. till I or 1.30 p.m., and that the Sectional Committees 

 should meet afterwards. Such an alteration would doubtless 

 mitigate the evils inseparable from the present system, and it is 

 to be hoped that a determined effort will be made at the ensuing 

 meeting to promote its adoption. A recommendation somewhat 

 to this effect was, I believe, made to the Council by at least one 

 of the Sections at the Birmingham meeting, but nothing came 

 of it. This is, perhaps, not surprising ; indeed, it is a question 

 whether anything ever does come of recommendations to the 

 Council — so some say. 



Machinery devised 50 odd years ago is no longer capable of 

 satisfactorily coping with modern requirements. We do not go 

 to British Association meetings to sit for hours together to hear 

 papers read such as we have listened to ad nauseam during the 

 previous sessions — our main object is to meet and exchange 

 views ; but everything seems to be done to prevent rather than 

 to promote this. Far fewer papers should be read ; far more 

 care should be devoted to the selection of papers ; much more 

 should be done to encourage discussion, especially between Sec- 

 tions ; and ample time and opportunity should be given for 

 conversation. 



The Sectional Committees are absurdly unwieldy bodies, and 

 in the case of some Sections, practically comprise the entire Sec- 

 tion : an appeal was made to the Council by my Section to put a 

 stop to a practice which enables all the nobodies to become mem- 

 bers of the Sectional Committee, but without result : I believe we 

 were told that we could do as we liked. Had this been the case, 

 we should scarcely have troubled the Council. The Sectional 

 officers, with at most half a dozen other members, would form 

 a far more useful Committee than any larger number ; but if it 

 be thought otherwise, let the whole Section sit as a Committee. 



Lastly, a word may be said as to the date of meeting. Could 

 any time be more unsuitable than the beginning of September? 

 Most of those who are engaged in advancing science are then 

 in the very middle of their holiday, and can attend only at grave 

 personal inconvenience. Henry E. Armstrong. 



NO. 1087, VOL. 42] 



The Mode of Obsetving the Phenomena of Earth- 

 quakes. 



The publication of Mr. Davison's paper "On the Study ol 

 Earthquakes in Great Britain," in Nature of the 7th inst. (p. 

 346) furnishes me with an opportunity of making a few remarks, 

 followed by a suggestion as to the mode of recording the effects 

 of seismic disturbances of the earth's crust on the apparent 

 change of position, especially of vertical objects, in the field of 

 vision of the observer. 



Remarks. — It will, I think, be admitted that the descriptions of 

 the alleged rocking to and fro of walls, towers, and chimneys, may 

 not unfrequently convey an exaggerated idea of what really takes 

 place ; and, probably, the same is true of the narratives of per- 

 sonal experiences of reeling or rolling movements on the part of the 

 narrator. I refer, of course, to the alleged extent of these move- 

 ments, for no one can doubt their actual occurrence as the result of 

 a tremblement de la terre. Such composite structures as walls, 

 towers, and chimneys have a real flexibility and elasticity, as is 

 shown, for example, by the opening and shutting up of cracks 

 and fissures in their substance. But the extremely vivid 

 accounts which we read of the swaying to and fro of solid 

 buildings, as witnessed by persons in the upright position, and 

 by others who are recumbent, suggest at least that some of these 

 recorded disturbances of position in external objects may be 

 more apparent than real, and may depend on some sudden un- 

 controllable movement of the head, and therefore of the optic 

 axes of the observer's eyes. 



It is well known that, when the head is moved swiftly to one 

 side and back again to a vertical position, upright objects, 

 seen in front, appear to shift from their vertical position in an 

 opposite direction, and then back again. It is not here needful 

 to explain scientifically this very obvious phenomenon. A 

 similar apparent displacement of objects, though in a vertical 

 direction, occurs when the head is nodded backwards and for- 

 wards. Movements of the head in intermediate directions pro- 

 duce intermediate effects ; whilst rotatory movements of the head 

 give rise to corresponding though mixed kinds of disturbance of 

 objects in the field of vision. Lastly, if the observer is in a 

 horizontal position, as in bed, for example, a suddenVolling over 

 of the head to one side and back again produces like phenomena. 



Now such disturbing movements of the optic axes must fre- 

 quently occur in the case of persons suddenly subjected to the 

 consequences of earthquake tremors, whether such persons are 

 in a vertical or in a recumbent position ; and it is difficult to- 

 understand how they should not occasionally seem to exaggerate 

 the apparent effects of the disturbance of the earth's surface and 

 the objects planted upon it. The equilibrium of the observer's 

 head is suddenly disturbed in a given direction, and an op- 

 posite involuntary movement instantly occurs in order to restore 

 the previous condition of things. Granting, then, the objective 

 reality of the swaying movements of vertical structures during 

 earthquakes, there seems to me to be reason to think that the 

 effect of these is occasionally enhanced, and their record in- 

 fluenced by the subjective impressions due to movements 

 occurring in the observer's own optical apparatus. 



Suggestion. — Supposing this view to be correct (though I can 

 furnish no direct proof of its truth from earthquake records), it 

 appears to me that the suggestion of which I spoke at the com- 

 mencement of this letter would be a useful addition to paragraph 

 («) of Section 2, Division A, of Mr. Davison's paper (p. 348), 

 which relates generally to the " situation of the observer." This 

 suggestion is that it should always be noted and stated towards 

 which point of the compass the observer's face was directed at the 

 moment of each observation, concerning the deflection of up- 

 right buildings, rocks, and so forth, especially of their lateral 

 deflections. For it is obvious that if a sufficient number of such 

 observations were recorded, it ought to happen, on my hypo- 

 thesis, that persons who looked across the earth-waves would be 

 moved up and down, and thus would have the vertical move- 

 ments only of objects in front of them exaggerated, whilst 

 persons who looked along the waves would be swayed sideways 

 by the undulations of the soil, and would therefore have the 

 extent of the lateral movements apparently increased. Under 

 the former condition, the " little hills " might appear to dance ; 

 in the latter case, cliffs, towers, walls, and chimneys might seem 

 to sway inordinately from side to side. 



Many such observations, duly recording the variations in the 

 apparent extent of the movements noted, together with the 

 positions of the observer as regards the compass, would, when 



