548 



NA TURE 



[April 4, 1S9: 



supposed, alihougb they often pa?s muster under erroneous 

 names. Tourmaline is sold as ruby, cinnamon stone as jacynlh, 

 white jirgoon and phenacite as diamond, while green garnets 

 are universally known in the trade as olivine or perilote. 



That the varieties of available gem-stones are not far more 

 numerous, is due mainly to the prejudice of purchasers, who 

 ring the changes on diamonds, rubies, sapphires, and emeralds, 

 and have heard of nothing else ; estimating the stones, as the 

 public estimates popular actors or authors, not by their real 

 excellence, but by their names. 



In the mineral gallery of the British Museum are many ex- 

 amples of cut stones which have rarely or never been employed 

 in jewellery, but should certainly win favour on their own 

 merits. 



One very curious example is a little gem cut from a crystal 

 of the ordinary tin-stone, the same ore which is worked for tin 

 in the Cornish mines. This is a stone which, when cut from a 

 su65ciently transparent crystal, possesses a most beautiful lustre 

 and colour. 



.•\s another example, I may mention a stone which, I suspect 

 from its appearance, would make a very beautiful gem. It was 

 sent with some other fragments from the ruby mines of Burmah ; 

 it is only a single rough fragment, and has completely puzzled 

 every one to whom I have shown it. By means of the very 

 tests which I have been describing, and without sacrificing 

 more than a pin's point of the stone, I have been able to identify 

 it as the boro-silicate of lime known as Danburite. This 

 mineral, if it has ever been used in jewellery, which is most 

 unlikely, has certainly never been rightly named. 



{.\ number of facetted stones lent by Mr. Gregory, who has 

 made many interesting experiments in this direction, were 

 thrown upon the screen by reflected light ; among these were 

 several of the less familiar gems, such as tourmaline, chryso- 

 beryl, phenacite, felspar, andalusite, axinile, spodumenc, 

 sphene, and idocrase. ) 



I do not know whether the final impression produced by 

 what I have said, is that the determination of stones is an easy 

 or a difficult thing. The impression which I wished to convey, 

 is that where these scientific lests can be applied, it is an abso- 

 lutely certain thing ; and where they cannot be applied, there 

 is no such certainty. 



The crystals from which these gems are cut are changeless 

 and imperishable, their beauty has been enhanced by the art of 

 man, but they have lost none of their wonderful properties in 

 the process ; in fact, it is only by utilising these very properties 

 that the lapidary converts them from dull stones to flashing 

 jewels, and it is by these properties that we have to recognise 

 them. 



The ruby formed countless ages ago in the heart of Burmah, is 

 the same thing in all essentials as the ruby formed to-day in a 

 Paris laboratory. 



It is curious to reflect that the diamond which to-day glitters 

 in a London ball-room, may have adorned the crown of some 

 Oriental monarch centuries ago — may have been picked from 

 the shores of an Indian stream in the dawn of civilisation — may 

 have been the silent witness of the growth and decay of empires 

 — but by its own unchanging existence has always borne stead- 

 fast evidence to the everlasting laws of nature. 



H. A. MiERS. 



THE OBSERVATION OF EARTH-WAVES 

 A.\'D VIBRATIONS. 



'T'HE object of this communication is to call attention to the 

 •^ apparently high velocity with which motion is transmitted 

 from an earthquake centre to places distant from it a (juarter 

 of the earth's circamferencc, and to the importance of instituting 

 an extended systematic observation of these movements. 



During the last few years Dr. li. von Rebeur-f'aschwitz and 

 other observers in Kuropc have recorded earth movements 

 which had their origin in Japan or in other distant countries. 

 Beyond a radius of a fc* hundred miles from thjir origin 

 these dis'.urbancci arc often too feeble t) be sensible or to be 

 recorded by ordin.iry seismographs. Their presence is, how- 

 ever, made known by the us; of specially contrived nearly 

 horizontal pendulum!, and by Ihcseandother instruments we find 

 lint they usually have a duration of from ten to thirty minutes, 

 tl.o jjh now ,ind then lliey la^t one nr two hours. On June 3, 



NO. 1327, VOL. 51] 



1S93, the writer obtained a record lasting 5 hrs. 24 min. In 

 Europe what was probably the same disturbance indicated a 

 movement which continued for about fifteen hours. From ob- 

 servations hitherto made, it seems extremely likely, as Dr. 

 E. von KebeurPaschwitz has suggested, that these earth-waves 

 could be recorded at almost any point upon ihe surface of our 

 globe, while the phenomena they present are such that it is 

 probable that their extended study would throw light, not only 

 upon the manner in which motion is transmitted through the 

 superficial portions of the earth, but also across its interior. 



As illustrative of the results to which these records lead, I 

 lake those derived from diagrams of several seismographs in 

 Tokyo, and from that of a long pendulum seismograph at Kocca 

 di Papa in Italy, which on March 22, 1S94, together wiili many 

 other instruments in Euiope, exhibited considerable motion. 

 The origin of the disturbance was off the N.E. coast of Vezo 

 (Lat. 42 X., Long. 146° E.). 



From observations made in Tokyo, distant about 600 miles 

 from the epicentrum, not only upon the initial disturbance, but 

 also four after-shocks, it seems that motion was propagated at 

 an average rate of about 2'3 km. per second. Inasmuch as the 

 instruments from which these records were obtained, are not 

 capable of recording movements of small amplitude, prob. 

 ably this velocity was that of the pronounced vibrations of 

 the ijuasi-elastic nature characteristic of most earthquakes. 

 There are reasons for believing that such waves outside an 

 epifocal area are practically confined to the surface of the earth. 

 A movement which from the manner in which it slowly afi^ected 

 ordinary or horizontal pendulum seismographs, had probably a 

 similar character, travelled from Japan to Italy with a velocity 

 of from 27 to 3 km. per second, the larger waves travelling at 

 the slower rale. 



Preceding these decided motions, minute tremors were ob- 

 served, which, if they originated at the epicentrum and 

 travelled on the surface of the earth, must have done so at a 

 rate of 115 km. per second, while if they were created by the 

 transformation of the energy of the partially elastic undulations 

 as they passed from medium to medium, then their velocity of 

 propagation inu5l have been still more abnormal. If it is 

 assumed that they reached Italy by direct radiation through the 

 earth, or that in consequence of refraction they followed cur- 

 vilincir paths, the observations indicate a velocity of 9 or 10 

 km. per second. 



Considering the influence of gravity upon the propagation of 

 surface undulations, the observed velocities may possibly be a 

 little lower than what might have been expected. The minute 

 tremors, hovever, seem to have a velocity which is roughly 

 twice that for a condensational raref.actional wave in glass. 



Observations upon other earthquakes, although none of them 

 can claim any great degree of accuracy, point to the same 

 general results. 



At present, the diversity of instruments employed in Europr. 

 and the various degrees of sensibility given to the few iiistru 

 ments which are approximately similar, apparently results in the 

 recording of ditTerent phases of motion, and it is not likely 

 that our knowledge will be increased or made more accurate 

 until there is greater uniformity in the methods ol observation. 

 Now to determine whether the disturbances created by large 

 earthquakes are propagated to distant localitic> in the manner 

 suggested, much might .be learned by establishing twelve or 

 fourteen similar instruments at an equal number of selected 

 stations round the northern hemisphere. It is yet premature 

 to indicate the class of instruments to be employed, but if 

 their chief function is to record the time of arrival and the 

 dilTercnt phases of these wide-spreading movements, it is the 

 writer's experience that many difticuliies may be avoided in 

 installation, adjustment and management, by using a type that 

 is not too sensitive to extremely minute changes ol level, such 

 as accompany fluctuations in temperature and changes in 

 atmospheric conditions. All of them should admit of ad- 

 justment to a similar degree of sensibility, and so lar as possible 

 be ailached to similar foundations in localities or places where 

 Ihe efl'ecls of tremor storms, which often eclipse the eflfects due 

 to earthquakes, are not likely to be pronounced. Photographic 

 surfaces on which records are received, should move at a rate 

 of iiol lea than two inches per hour, which will enable an 

 observer to determine time intervals to within 30 seconds. 



It would seem advisable that the first attempt to inake a 

 seismic survey of the world should be tentative. Having ob- 



