280 



SCIENCE 



[N. S. Vol. XXVIII. No. 713 



barometric pressure, time of day, time of year 

 and weather upon earthquakes, but each of 

 these is considered separately, while it is only 

 by combination that they are rendered ef- 

 fective. Falb, in a very studious work rarely 

 quoted,' considers the luni-solar combinations 

 with conclusions favorable to their coinci- 

 dence with seismic movements, but the aggre- 

 gate conclusions of all who have examined the 

 subject do not form a definite and harmonious 

 result. I believe this to be due in part to the 

 very elaborateness of the methods used in 

 treating an essentially simple subject and to 

 taking into consideration a great number of 

 very slight earthquakes and eruptive phases 

 whose entry into the calculation has led to 

 erroneous conclusions — it is like including the 

 mortality of infants in computing the length 

 of human life. I propose, therefore, in this 

 paper, to make a preliminary examination of 

 the subject as it has developed under my own 

 studies during the past two years. 



It will be impossible, however, to enter at 

 this time into an exhaustive study of all the 

 possible manifestations or transformations of 

 energy by which the luni-solar influence may 

 affect terrestrial volcanism— tidal action, 

 atmospheric electric potential, electro-mag- 

 netic telluric currents, etc.— but, without ex- 

 cluding these, we may for the present simplify 

 our conception of the influence by consider- 

 ing it as productive of a gravitational dis- 

 turbance of the terrestrial mosaic. Imagine 

 such a body as the earth subjected to the 

 varying attraction of the sun and moon, now 

 on one side of both, now revolving between 

 the two like the armature of a giant dynamo 

 in its field of magnetic force; with the moon 

 in such close proximity as to exert a consider- 

 able difference in attractive force at the earth's 

 center and at the nearest and farthest periph- 

 eral points and with an orbit so elliptical 

 as to vary its distance by a factor of more 

 than one tenth. And then consider that in the 

 crust of this revolving earth sphere there exist 

 volcanoes, which are at times in a condition 

 of potential eruption and rock strata in a con- 



' " Grundziige zu einer Teorie der Erdbeben und 

 Vulkanausbniche," Rudolf Falb, 1869. 



dition of stress amounting to potential fault- 

 ing, and it will readily be seen how small is 

 the power required to touch off these little ac- 

 cumulations of latent energy in proportion to 

 the enormous forces involved. Note that the 

 celestial influence is here considered as being 

 exerted merely in the releasing of stored 

 energy and not as being directly concerned in 

 the accumulation of the latent forces. Note 

 also that we have now cast off the restriction 

 imposed earlier in this paper as to the type of 

 volcano to be considered, all types being 

 affected by the external influence. 



Let us now consider in detail that which we 

 have defined as " gravitational disturbance." 

 When the sun and moon are in line with the 

 earth, their combined attraction tends to de- 

 form the earth sphere to an ellipse — the tend- 

 ency is resisted and a condition of stress 

 results. When in quadrature their influence 

 is largely neutralized and these changes, in 

 connection with the earth's diurnal rotation, 

 may be considered as the basis of the gravita- 

 tional disturbance. 



The greatest luni-solar gravitational effect, 

 for these latitudes, wiU be produced when the 

 sun and moon are at opposite ends of a diam- 

 eter through the earth's center (opposition) 

 and having a north and south declination re- 

 spectively of 23° (solstice) and with the moon 

 in perigee. These positions would also tend 

 to produce the greatest ocean tides, but we 

 should avoid considering this influence on the 

 basis of tidal action — it is because of this, in 

 my opinion, that much misunderstanding has 

 arisen. We have not to do with a liquid 

 ocean, where, under luni-solar attraction, a 

 moving wave-form would produce, at the times 

 of maximum effect, very high and very low 

 tides, but we must consider a mosaic globe 

 composed for the most part of solid materials 

 in which the effects, although not of such 

 amplitude as to be visible, will be more power- 

 ful and less ephemeral. We may imagine the 

 mean luni-solar effect upon the earth during 

 the several days of each favorable position to 

 be a tendency to positive deformation of the 

 sphere. This will result in a diminution of 

 lateral pressures due to terrestrial gravitation 



