NATURE 



[March 23, 1899 



and distortional vibrations through our globe, and the 

 rate of transmission of the former is closely connected 

 with the average depth of the path along which they 

 have travelled. When our observations on these move- 

 ments are more exact and numerous, we shall then know 

 more than we do at present about certain physical 

 characteristics of the planet on which we live. 



At Utrecht, Potsdam and W'ilhelmshaven, these unfelt 

 movements frequently correspond in time with well- 

 marked perturbations of magnetic needles, but inasmuch 

 as similar needles are not disturbed at other stations, we 

 are not quite certain that the observed irregularities in 

 magnetograms are altogether the result of mechanical 

 disturbance. 



Then, again, we have the curious observation that at 

 certain magnetic observatories prior to great earthquakes 

 originating in their vicinity there have been uneasy 

 movements in magnetic needles. When considering 

 whether these observations are merely accidental co- 

 incidences, we must remember that the initial impulse or 

 impulses of these disturbances ha\e been sufficient to 

 cause our world to palpitate from pole to pole, that they 

 have sometimes been accompanied by bodily displace- 

 ments of material sufficiently large to set the Pacific 

 Ocean in a state of oscillation for many hours, and that 

 the displaced material is in every probability highly 

 charged with magnetite. We do not know the nature of 

 the changes which were taking place in this material 

 before its rupture, but we see in the final movement a 

 possibility of sudden local magnetic disturbance. 



Other possible connections between the movements of 

 magnetic needles and those of horizontal pendulums lie 

 in the facts that each have diurnal movements, and each 

 may e.xhibit continuous or nearly continuous movement. 

 The diurnal movements of horizontal pendulums are 

 closely connected with effects accompanying solar 

 radiation. The late Dr. Reinhold Ehlert, of Strassburg, 

 saw in some of these a world distortion ; whilst in others, 

 my own observation leads to the supposition that their 

 explanation is to be found in changes of surface-load 

 brought about by evaporation, condensation, precipita- 

 tion, and transpiration of moisture. To account for the 

 almost unbroken continuity of earth tremors we are at a 

 loss ; but when we reineniber that in the world there is 

 upon the average an earthquake occurring every half- 

 hour which might be recorded, that probably there are 

 many taking place beneath the sea and deep in our earth 

 which are never felt, it does not seem unreasonable to 

 look for their explanation in the vibrations accompanying 

 these frequent adjustments in operation within the earth. 

 If it is admitted that these continually moving materials 

 are magnetic, not only do they suggest an explanation 

 for the minute sinuosities on magnetograms, but they 

 also indicate a possible relationship between hypogenic 

 geological activity and secular magnetic changes. 



In Jajjan, built up as it is round a core of rocks 

 saturated with magnetite, which in their deeper portions 

 are intensely hot, and therefore probably possess a 

 reduced magnetic susceptibility, these earth tremors are 

 apparently, and as we should expect them to be, more 

 pronounced than they are in England or Europe. As to 

 whether \\\<t frctilleinenls ow the magnetograms from that 

 country are more frequent and distinct than those taken 

 under similar conditions in non-volcanic countries, I 

 leave to be answered by those who have the means of 

 making the necessary comparisons. 



That the records from a seismological observatory 

 throw light upon sudden movements of magnetic needles 

 at certain observatories is an established fact ; but 

 whether the bond connecting magnetic observations and 

 those obtained by the seismologist is closer than is 

 usually admitted, is apparently a matter worthy of con- 

 sideration. 



NO. 1534, VOL. 59] 



From a series of seismograms obtained from differen 

 stations we should be in a position to locate the site o 

 sub-oceanic changes, and determine positions to bi 

 avoided by the cable engineer. .A single seismogran 

 may often set our minds at rest as to the cause leading, 

 to cable interruption, a matter of special importance to 

 isolated Colonies, w hilst it has repeatedly been the means 

 of extending, confirming, or disprox ing ordinary tele- 

 graphic information. Another class of observations to 

 which the seismologist devotes his attention are those 

 indicating secular, seasonal and irregular changes in the 

 vertical, which are of importance to the astronomer, 

 earth pulsations and a variety of instrumental move- 

 ments, the cause of which is not yet clear. 



.■\lthough all the above-mentioned investigations can 

 be carried out at a single observatory, the results to 

 which they lead are by no means of equal value. For 

 example, should we wish to know the velocities with 

 which the vibrations of a given earthquake have been 

 propagated along various paths through our earth, it is 

 evidently necessary to have the means of making com- 

 parisons between seismograms obtained from similar 

 instruments at widely separated stations. It is a pleasure 

 to state that the necessary co-operation here indicated 

 has been obtained, and in response to an invitation 

 issued by a Committee of the British Association, the 

 directors of observatories at the following places ha\e 

 kindly undertaken to make the necessary observations ; 

 Kew, Paisley, San Fernando Cadiz,!, Cairo, Beirut, Cape 

 of Good Hope, Mauritius, Madras, Calcutta, Bombay, 

 Batavia, Tokio, two in New Zealand, Cordova 

 (Argentina, Honolulu, Victoria (B.C.), Toronto, Phila- 

 delphia, .Arequipa, Mexico, Trinidad. Certain of these 

 are already sending in records. 



What is now required in Great Britain is not simply a 

 central office where these records can be examined, but 

 also a station at which a variety of seismological observ- 

 ations can be made which will be comparable with the 

 records from corres])onding instruments similarly installed 

 in other localities. As illustrative of this, although it 

 would be extremely interesting to note the varymg effects 

 of barometrical pressure upon the plains of Lincolnshire, 

 and to compare the magnitude and period of earthquake 

 waves as recorded there with those recorded on a rocky 

 surface, it is extremely probable that the records of 

 diurnal waves from such surfaces, or in fact from any two, 

 but different alluvial or soft foundations, would only yield 

 results of local value. Any haphazard selection of a site 

 for a laboratory might take us to a place where we might 

 find an apparent diurnal or other variation in gravity, 

 and where the same gold bead upon an assayers balance 

 rapidly changing its zero, might appear to have a different 

 weight at different times. Then, again, if we wish to 

 study the continuous trembling of our earth, we require 

 to be on solid materials at least half a mile from a rail- 

 way, and some distance from any source of artificially 

 produced \ ibration. If in addition to this it should ever 

 be found desir;ible to obtain a highly magnified record of 

 the movements of a magnetic needle, it is obvious that 

 we must be far removed from the possibility of electrical 

 disturbance. 



What is required, and especially for earthquake 

 recording, is a platform or foundation which continues 

 downwards ;is a uniform mass into the interior of the 

 earth. .Such conditions may probably be met with upon 

 certain granite bosses, but it is likely that the greatest 

 continuity would be found upon an old volcanic neck, of 

 which we ha\c very many illustrations in these islands. 

 Although those are mere coup li'cpiiu^lcs in the crust of 

 our earth, it is not unlikely, especially when their lateral 

 dimensions increase with depth, that they convey more 

 vibrational energy to the surface than is conveyed 

 through discontinuous sedimentary strata. 



