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NATURE 



\yuly 25, 1889 



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. ] 



Coral Reefs. 



With reference to Captain Moore's two difficulties, T have to 

 say : — (i) The position of banks around islands depends, in my 

 opinion, on the nature of the rocks ; loose material, or easily dis- 

 integrated rock, may be found either on the lee or weather side 

 of an island. There are many examples of these banks in all 

 positions around islands where there are no coral reefs. (2) I do 

 not think it is the case that corals reach the surface simultaneously 

 on all sides. What Captain Moore refers to as sunken reefs is 

 good evidence that they do not. The great uniformity in the 

 breadth of the reefs in some regions is, according to my view, 

 due to the play between the forces secreting and depositing car- 

 bonate of lime, and those engaged in its disintegration and 

 solution whenever the organisms have died. Reefs are very often 

 non-continuous, as Captain Moore himself points out in the case 

 of the Barrier Reef of Australia. This, too, I have explained in 

 the same way, but taking into account local conditions. I cannot 

 admit Captain Moore's supposition about the filling up of the 

 lagoon around Solo, nor his explanation of the bank to the west 

 of Ono. I have no charts with me here, so cannot at present 

 refer to the other illustrations he has given. 



Grangemuir, Pittenweem. John Murray. 



An Earthquake ? 



On Friday, July 5, the inhabitants of Lyme Regis were much 

 astonished by some noises, which took place at intervals 

 between 11 and 11. 15 p.m., and which there seems good 

 reason to believe were caused by an earthquake. In three 

 houses the occupiers thought that heavy pieces of furniture 

 -were being moved about, which was of course found not to 

 be the case ; and in another the inmates thought at first 

 that something was wrong with the kitchen boiler. The noises 

 observed consisted of a distant rumble which grew nearer till at 

 last the windows of the houses rattled, and in some cases distinct 

 vibrations of the houses were felt. Some have supposed that 

 these noises were caused by guns at sea, but this seems impos- 

 sible, because (i) the rattling of the windows occurred after the 

 distant rumble, and not simultaneously as would have been the 

 case with guns ; (2) a gentleman who has had much experience 

 in guns and firing, has declared that the noise was not like guns ; 

 (3) after making enquiries we have been unable to discover that 

 any firing at sea took place that night ; (4) although the night 

 was still, a heavy ground swell was observed. These phenomena 

 have not received any notice as far as we know in the public 

 press, and it seems a pity, if an earthquake, as we believe, really 

 took place, that there should not be some record of it. 



Lyme, A. R. Sharpe. 



i*he Excursion to the Volcanoes of Italy. 



Thanking you for noting the intended excursion of geologists 

 to the active and extinct Italian volcanoes under the auspices of 

 the Geologists' Association and Geological Society of London, 

 I would like to draw the attention of your readers to the remark- 

 able changes at Stromboli which have lately occurred. New 

 eruptive mouths have opened, and there has been an outflow of 

 lava, a phenomenon so far unknown (so far as recorded) from 

 20CO to 3000 years. There is an uncertain reference to such an 

 occurrence, but the change at Stromboli from Strombolian to 

 Vesuvian activity is remarkable. I am also informed that the 

 eruption of Vulcano still continues with paroxysms of greater 

 activity. Thus the excursionists will have the advantage of see- 

 ing changes that, even for a constant resident in such a region, 

 are rare. H. J. Johnston-Lavis. 



Naples, July 15. 



Seismology in Italy. 



I was glad to see that Prof. Grablovitz had laid claim to atten- 

 tion for some of his other memoirs which I had not at that time 

 seen, and which are of much value. I would especially draw the. 



attention of seismologists to his study of the relationship of tem- 

 perature and outflow of a thermo-mineral spring at Porto 

 d'Ischia to the tides and barometric pressure. 



In my article I only reviewed those memoirs placed in my 

 hands by the Editor of Nature, or sent to me privately. I may, 

 however, say that as near as possible a complete review of all the 

 papers on seismology and vulcanology published during 1888 is 

 being prepared by me for the Annuaire Geologique Universel of 

 this year. I should therefore be glad to receive any other papers 

 on those subjects, that have not been sent to me, as soon as 

 possible. H. J. Johnston-Lavis. 



Naples, July 15. 



The Earthquake of Tokio, April 18, i88g. 



Reading the report on this earthquake in Nature (June 13, 

 p. 162), I was struck by its coincidence in time with a very 

 singular perturbation registered by two delicate horizontal pen- 

 dulums at the Observatories of Potsdam and Wilhelmshayen. 

 These instruments, which represent, with some modification, 

 Prof. ZoUner's horizontal pendulum, were established in March 

 1889, for studying the slight movements of the ground. 

 The motion of the pendulum, which is left to oscillate freely 

 whenever its equilibrium is disturbed, is registered by the same 

 photographic method as that employed for magnetic observa- 

 tions. The pendulum is in the plane of the meridian, so that 

 any shock, the direction of which is not in this plan-e, will pro- 

 duce oscillations of the pendulum, diminishing gradually, if it 

 is left undisturbed after the shock. The pillars supporting the 

 instruments are fixed in a depth of i metre below the ground of 

 the cellar which was chosen as a suitable place for the erection 

 of the instrument. 



During the three months from April to June, the disturbance 

 of April 17, i8h. G.M.T., was the most remarkable which oc- 

 curred The following readings of Greenwich mean time, which 

 are best explained by the accompanying figures, are taken from 

 the original photographs ; it must, however, be mentioned that 

 the small scale of 11 millimetres per hour does not allow a very 

 accurate determination of time, and that an error of one minute 

 or two is quite probable. 



(i) Potsdam. — \%Z(), April 17. From 5h. until I7h. 2im., 

 great steadiness of image. 



h. m. 



17 21 First traces of disturbance. 



17 39 Beginning of small oscillations. 



17 54*3 Motion suddenly increases and reaches its maximum 



at 



18 I Amplitude of oscillation 154 millimetres. The 



amplitude then suddenly diminishes. 



18 43) 



18 58 > Maxima of oscdlation. 



19 45) 



20 o Perfect steadiness of image. 



(2) Wilhelmshaven. — Here, also, the image is perfectly steady 

 until i7h. 30m. 



h. m. 



17 30 Beginning of small oscillations. 



17 48-17 51 A short interval of perfect steadiness. 



17 51 The movement suddenly increased, and as the light 



is not strong enough to mark the single oscilla- 

 tions, the image disappears until 



18 38 when the principal disturbance reaches its end. 



-'l\ 



^^ \ Maxima of small oscillations. 



19 22 i 



20 2 ; 



20 7 Perfect steadiness. 



If we compare these dates, it seems most probable that the 

 momert which shows a sudden increase of motion, and is best 

 marked on the curves, may be considered as the beginning of 

 the principal disturbance. We thus have — 



For Potsdam I7h. 54-3™. iMean, I7h. 527^.. 



For Wilhelmshaven... I7h. 51m, / ' ' -^ ' 



which, considering the error of the readings, may be taken as 

 one and the same moment. 



The beginning of the earthquake of Tokio was observed at 

 2h. 77m, Tokio M.T. The difference of longitude (taken from 

 a map) being gh. 19 "Sm. E., we find that the shock occurred at 

 i6h. 48-4m. G.M.T. on April 17, and thus it took ih. 4-3m. 

 to travel across the body of the earth. 



