FEa G, 1885.] 



♦ KNOWLEDGE * 



99 





J5TRATED 1^ S 



. /;iNEoFSqENCE 



.AINDrWORDED-EXACTIYDESCEiBED. 



LONDOF: FRIDAY, FEB. 6, 1885. 



Contexts of No. 171. 



riGi 



On Some C«uses of EArthqaakes. 



Bt Richard A. Proctor 99 



The Philosophv of Clothing. I. By 



W. Mattifu Willisn s 100 



Otlr Two Bnuns. Bj Richard A. 



Proctor 101 



The Touns Electrician. {IUh4.) 



By W. Slin»o 102 



Oa Termiies. By Surgeon-General 



Hutchinson 103 



'^Iher Worlds than Ours 105 



Chapters on Modem Domestic Eco> 



nomT 105 



The Weight of Knrines 106 



TAGS 



Thought and Language. III. By 



AduS. Ballin 107 



The Refomiation in Time-Keeping. 



aUii'.) By W. F. Allen 108 



Editorial Gossip 108 



Reviews 110 



The InQuence of Civilisation on 



Eyesight 112 



Miscel anea 112 



Correspondence : The Psychology of',Tri; 

 Instinct — Our Two Brains — Ques- 

 tion from Flnlland, ic 113 



Our Inventors' Column 117 



Our Chess Column US 



OX SOME CAUSES OF EARTHQUAKES. 



Bv RicnAiiD A. Proctor. 



IT has been noticed that the Spanish earthquate.s have 

 been followed by hurricanes, and many are asking hew 

 earthquakes can cause hurricanes. " When an eaithqua''e 

 is succeeded by a hurricane," says the Nev) York I'ribur v, 

 "the inference must be that if the occurrence of the wini 

 storm is more than a coincidence, it must be caused by a 

 profound atmospheric change of pressure, such a change 

 as could only be produced probably by an electrical storm 

 of exceeding violence." Tiiis I only quote to show how 

 the question has been raised on the American side of 

 the Atlantic Of electricity, one may say what Laplace 

 said about the theory of special interference of the 

 Almighty as an explanation of unusual phenomena — " Qa 

 fxplique beaucoup de choses." It does not seem to have 

 been noticed that the Spanish earthquakes followed a 

 remarkable series of Atlantic storm?, and that these 

 earthquakes have continued since the great hurricanes 

 occurred which drove the Tribune to the all-explaining 

 electrical theory. 



If we consider the matter with a little attention, we 

 shall cease to wonder that great atmospheric disturbances 

 excite subterranean activity. The efl'ects of what seem 

 slight changes of atmospheric pressure must in reality be 

 enormous in modifying the {nessures underneath the 

 earth's crust. The barometer often ranges halfin-inch in 

 height without any great hurricanes following. Taking 

 such a change as this, and supposing that over an area as 

 large as the Britit^h Isles, and with the seas between them 

 — say, in round number.-', 100,000 sijuare miles — the baro- 

 meter stands at 29| in., while on either side, over a similar 

 area, the barometric column has an average height of 

 29| in. ; let us consider -what difference of pressure is 

 involved, and what are the changes produced if the 

 barometric column is raised half an-inch over the British 

 area, and lowered by half-an-inch over the adjacent 

 areas. The jiressure of the air on a square inch, when 

 the barometer stands at 30 in., is nearly 15 lb., so that 

 a fall of half-an-inch (one-sixtieth of thirty) means a reduc- 

 tion of [ressure by nearly a qnarterof a-pound tothefquare 



a square mile 

 and the pies- 

 no less than 

 jiart too great, 



inch. (Or, of course, we may leave the air out of the 

 (luostion, and simply weigh a half-inch of mercury in 

 height on a s-quaro inch biisc ; this will be one 3,150th 

 part of a cubic foot of mercury, and every one knows 

 that a cubic foot of mercury weighs SIS lb. ; the 3,l5Gth 

 part of 818 x IG oz is 3:!Joz) Now, in a square yard 

 there are 1,290 square inches, and in a square mile about 

 3,000,000 square yards. Therefore, at a (juartcr of a lb. 

 to the square inch, the pressure on 

 amounts to 321 times .3,000,0001b., 

 sure on 100,000 square miles to 

 97,200,000,000,000 lb. This is 1-5 1 th 

 because the pressure on a square inch is only 5.3 51 ths of 

 i oz. Knock od' then a 5 1th part, getting for the actual 

 diti'erence of pressure due to a half-inch rise or fall of tlio 

 mercurial barometer 95,450,000,000,0001b., or in round 

 numbers 42,000,000,000 tons. Can it be .suppo.^ed to be a 

 slight matter if, as frequently happen.'*, such an enormous 

 pressure as this is thrown upon the area of the British 

 Isles and tha seas around and between them, in the course 

 of a few hours, while adjacent areas are relieved of a cor- 

 responding weight, and then a few hours later the adjacent 

 areas are oppres.sid by having many thousands of millions 

 of tons extra weight thrown upon then), while the pressure 

 on the British Isles is diminished in the same tremendous 

 degree '! We hear it sometimes described as a remarkable 

 thing that great barometric changes are followed by signs 

 of disturbances in British mines ; but when we see that 

 only a moderate and normal change of atmospheric pressure 

 means many thousands of millions of tons added to the 

 pressure on the earth's crust in and around Great Britain, 

 or deducted from that pressure, the wonder seems rather to 

 be tliat changes so slight are produced by pressures so 

 enormous. 



Now the disturbed areas in the hurricanes of last 

 DeceniVjer were very much larger than those I ha\eju.st 

 considered, and the differences of atmospheric juessure 

 much more remarkable. The areas of diminished pressure 

 were probably not less than 500,000 square mih s. and the 

 surrounding areas of increased pressure fully as large, 

 while the range of the barometer was in some cases fully 

 2 inches. This would make the weights added to and 

 taken away from the disturbed areas, sometimes very 

 quickly, no less than a thousand billions of tons. Can 

 we wonder if parts of the earth where the crust is re- 

 latively weak and unstable should show the effects of such 

 tremendous changes of pressure as these ? 



But this is not all. The seas respond to the action of 

 mighty huriicanes, not only by being tossed into waves 

 (which in tlie open sea are mere risings and fallings of 

 masses of wat» r not themselves carried along), but by 

 being carried in large massts before the winds. Every, 

 one knows how a moderate tide is changed into a very 

 high tide Viy favouring wind.s, while an expected very 

 high tide becomes a moderate tide when the wind opposes 

 the influx of the water. Along a shoi r-line such 

 as that presented by the Spanish Peninsi !a toward;! 

 the west the water must often be raised two or 

 three feet above its normal level by the action ci 

 lorg-continued strong winds from the west. Now, con- 

 gider one hundred miles of .shore-line, and the effects of a 

 rise of the sea by only one foot on account of westerly 

 hunicanes, that rise extending only ten miles out to sea. 

 We have then a thousand square miles of water, one foot 

 deep, as the extra pressure npon the crust under that 

 shore-line. Tnis gives 27,000 millions of cubic feet of 

 water, each cubic foot weighing 1,000 oz., or in round 

 numbers ab mt 750 millions of tons of extra water tlircnu 

 on a shorr-line on'y a hundred miles in '»>i gth. Alorg 



