Trof. John Milne — On Earth Movements. 483 



Of late we have learnt much about earth tremors from Messrs. 

 George and Horace Darwin, who, while endeavouring to measure 

 the lunar disturbance of gravity, have shown us that even in Britain 

 we have a soil which is subject to storms of microscopic earth- 

 quakes. These disturbances were so numerous and of such a mag- 

 nitude that they eclipsed the results which were being sought 

 for, and the problem of experimentally measuring the pull exerted 

 by the moon had to be relinquished. In Japan microscopic move- 

 ments of like character have been recorded with apparatus similar 

 in principle to that employed by Messrs. Darwin. Among the 

 earliest work done in the investigation of these minute movements 

 was that inaugurated by Timoteo Bertelli, of Florence, who, in 

 3870, announced that he had perceived the earthquakes which shook 

 Eoniagna, although to ordinary observers in Florence these move- 

 ments had not been perceptible. Although doubt was cast upon 

 Bertelli's work, it appears to have been the origin of a series of 

 microseismical observations, a distinguished leader in which is Pro- 

 fessor M. S. de Kossi, who told us in 1874 that almost all large 

 earthquakes were preceded by microseismio storms. Another re- 

 sult which has been announced is that the microseismic motions 

 increase with the fall of the barometer. A third result is that 

 these disturbances are sometimes simultaneously recorded through- 

 out the whole of the Italian Peninsula. 



These and other equally interesting results have already been 

 more or less clearly established, and the object in here mentioning 

 them is practically to show that earth tremors may have a real and 

 possibly a universal existence. It may not have occurred, perhaps, 

 to many Englishmen that the mountains and plains on which they 

 dwell are probably in a state of perpetual vibration ; that England 

 is, in fact, quivei'ing like a mass of jelly in a spoon ; that there is 

 a continuous tremulous motion going on everywhere in the earth. In 

 earth tremors we have one of the most universal of nature's pheno- 

 mena,, and one which has hitherto been almost entirely overlooked. 



From accidental observation and from direct experiments we 

 know earthquakes can produce electrical phenomena of alarming 

 magnitude in our telegraph lines and cables. May we not, then, 

 ask what is the connexion between earth currents so observed and 

 microseismic storms? Are they connected with disturbances in the 

 earth's magnetism which are being so studiously recorded in all 

 accessible parts of the globe ? Do they hold any relation to varia- 

 tion in earth temperature ? In short, what are these movements, 

 and what connexion have they with phenomena exerting an influence 

 upon our every-day existence? 



To science the observation of these disturbances opens a new 

 realm for investigation. The observations made in Italy apparently 

 indicate that they may hold some relation to the rising and sinking 

 of our land which Mr. George Darwin, in his last report to the 

 British Association, has shown is a consequence of barometrical 

 variation. Their maxima may, perhaps, be related to the elastic 

 tides of the earth's crust, and, therefore, they may be as periodic as 



