January 2, 1902] 



NA TURE 



Inasmuch as these surface-waves could be recognised 

 at a distance of a few hundred miles from their origin, 

 it was naturally assumed that the movements resulting 

 from unusually large disturbances which not unfrequently 

 travel to their antipodes should exhibit the same undu- 

 lating characteristics. Some support to this view was 

 found in the large movements of delicately adjusted 

 horizontal pendulums, the movements recorded in the 

 traces from magnetographs and barographs, whilst the 

 movements occasionally noted of the bubbles in astro- 

 nomical levels or the shifting of a star in a telescopic 

 field, together with other phenomena, tended to strengthen 

 the view that the large waves in seismograms represented 

 actual earth tilting. Although I do not yet see how 

 certain of these phenomena can be explained on the 

 assumption of purely horizontal movements, especially 

 when the period of these may exceed twenty seconds, in a 

 British .•\ssociation Report i. September igoo) I published 

 observations indicating that the surface-wa\e theory met 

 witn so many objections that it could not be generally 

 applied. One objection rested upon observations indi- 

 cating that the velocity of propagation of these waves did 

 not appear to be constant. 



Although for certain practical purposes it may be 

 assumed that the arcual velocity of these movements is 

 3 km. per second, there is evidence to show that they 

 have an initial velocity of about 2 km., whilst their quad- 

 rantal velocity approaches 4 km. per second. Dr. C. G. 

 Knott, who has done so much for practical and theoretical 

 seismology, at once pointed out that any change in speed 

 was a serious stumbling-block to the surface-wave theory, 

 which he had always regarded with disfavour. As an 

 alternative, in the ScottisJi Gcon^raphical Magazine 

 (January 1899), and in other publications, he showed that 

 the observations relating to speed could be satisfied by 

 the assumption of a distortional mass wave, and it is to 

 the outcrop of such waves towhich Dr. Knott looked for the 

 explanation of the large movements of the seismograph. 



This hypothesis, however, does not tell us whether the 

 movements actuating a seismograph are vertical, hori- 

 zontal or angular. Many years ago Dr. A. Cancani 

 pointed out that if these waves represent tilting, from the 

 angular values of the same and the length of the waves 

 which can be deduced from their period and velocity, 

 then on the assumption of simple harmonic motion the 

 height of such waxes could be calculated. 



Such heights ha\e been frequently estimated, but in 

 the British .-Vssociation Report (September 1900), p. 83, 

 attention is called to the fact that as these represent 

 accelerations not unfrequently I, 50 of gravity, the exist- 

 ence of these vertical displacements is doubtful, and an 

 experiment to confirm or modify our views was in 

 progress. 



The "experiment " referred to consisted in observing 

 the movements of a pointer attached to the earth rela- 

 tively to the pointer of a clinograph similar to, but much 

 larger than, the one described above. Any relative move- 

 ment of these pointers would be shown by the displace- 

 ment of a spot of light reflected from a mirror hung by a 

 bifilar attachment to the two pointers. Subsequently the 

 record was made mechanical. With the first installation 

 I mm. deflection =o"7, and in the second 6"o. Although 

 several large earthquakes occurred, no record was 

 obtained. 



In another experiment slight records were obtained 

 from the photographic registration of a spot of light 

 reflected from a mirror which was caused to rotate by 

 the rising or falling of a weight attached to an ordinary 

 spiral spring. The length of the spring under the in- 

 fluence of its own weight is 9'5 inches. With a load of 

 I lb. S ozs. its length was 3 feet 5 inches and its natural 

 period 2 seconds. 



The earthquake of October 9, 1900, caused ripples on 

 the photogram each about '5 mm. in range, which would 



NO. 1679, VOL. 65] 



correspond to a change that might have been produced 

 by increasing and decreasing the load by i 700 part of 

 itself. The period of motion was approximately 6'5 

 minutes, which corresponded with the period of maxima 

 in the large waves as in an ordinary seismogram. 



The \'enezuela earthquake of October 29 gave deflec- 

 tions of half the above and with periods of about 

 7 minutes. Other earthquakes caused somewhat similar 

 movements, but usually nothing more than slight blurs 

 upon the photographic traces were to be seen. 



The records from the clinometer indicate that earth 

 tilting has not been measurable by the instrument em- 

 ployed, whilst the records from the spiral spring show 

 that there is a possibility that vertical motion may exist, 

 but if it does it is exceedingly minute. 



The general inference is that the large waves due to 

 earthquakes originating at a distance, whether they are 

 surface waves or mass waves, actuate horizontal pen- 

 dulums by horizontal displacements of the ground, rather 

 than by the tilting of the same. _ 



The distinguished seismologist. Dr. F. Omori (see 

 " Publications of the Earthquake Investigation Com- 

 mittee," Tokyo, No. 5, January, 1901), and Dr. Wilhelm 

 Schliitter (see his " Inaugural Dissertation," Gottingen, 

 1901) have recently expressed similar views. Dr. Omori's 

 objection to the surface-wave theory is based partly upon 

 the impossibility of accepting the vertical accelerations- 

 calculated on the assumption that seismographs have 

 acted as clinometers, a view already expressed by Dr. 

 C. G. Knott, Dr. C . Davidson, myself and other physicists, 

 and partly upon the observations he has made showing 

 that the amplitude of seismograms depends upon the 

 multiplication of the writing pointers rather than the 

 sensiljilities of seismographs to tilting. 



Dr. Schlutter's conclusions are arrived at from the fact 

 that some twenty earthquakes failed to yield any record 

 on the photograms obtained from a ''klinograph," which 

 in general arrangement is not unlike those already re- 

 ferred to, but very much more sensitive. The care which 

 Dr. Schliitter took to ensure accuracy can only be realised 

 by reference to his memoir, which, as an essay relating 

 to this class of investigation, stuuAs Jaa'/c p)-n!ieps. 



The general conclusions arrived at are that for severe 

 earthquakes with a near origin, surface earth-waves may 

 be marked. To record these clinographs are required, 

 and the entries in registers referring to the same should 

 be correspondingly modified. In designing instruments 

 to record earthquakes with a distant origin, the principle 

 introduced by Prof. J. A. Ewing into seismometry re- 

 lating to steady points must be carefully observed, and 

 in our registers we must regard our entries as referring 

 to displacements which are horizontal rather than angular. 



J. Milne. 



ELEMENTARY MEDICAL EDUCATION. 

 WfE. have received a memorial to the General Medical 

 '* Council concerning the relegation of the teaching 

 of elementary chemistry, physics and biology to the school, 

 as distinguished from the medical school. The memorial 

 is signed by a number of men of science, teachers of 

 botany, zoology, chemistry or physics. In the opinion of 

 these gentlemen the above subjects should be per- 

 manently retained as part of the medical curriculurr; 

 proper, and their relegation to the schools is, according 

 to them, likely to have a prejudicial influence upon 

 medical education. The most powerful argument, so far 

 as we can see, brought forward in support of this 

 hypothesis is that the schoolboy, as distinguished from 

 the medical student, is intellectually less capable of 

 grasping those scientific generalisations without which the 

 teaching of the elementary scientific subjects above named 

 would not be productive of the desired result, viz. the 



