372 THE POPULAR SCIENCE MONTHLY. 



through fully two inches, and a pool of mercury two inches deep and 

 a square foot in area weighs 145 pounds ; hence, when the barometer 

 is very high, every square foot of the earth-surface supports about 140 

 pounds more than if it is low ; and 140 pounds to the square foot is 

 1,800,000 tons to the square mile. 



Now, rocks are not absolutely rigid against flexure, certainly less 

 so than most of the metals, and these enormous weights have to be sup- 

 ported by the rocks. Taking a probable estimate for the elasticity of 

 rocks, I have made some calculations as to the amount of effect that 

 we may expect from this shifting of weights, and I find that it is 

 likely that we are at least three or four inches nearer the earth's 

 center when the barometer is very high than when it is very low.* 



It may be that the incessant straining and unstraining of the earth's 

 surface is partly the cause of earth -tremors, and we can at least under- 

 stand that these strains may well play the part of the trigger for 

 precipitating the explosion of the internal seismic forces. The calcula- 

 tions also show that near the sea-coast the soil must be tilted toward 

 the sea at high-water, and that the angle of tilting may be such as 

 could be detected by a delicate instrument like that of M. d'Abbadie. 



This breathing of the solid earth seems to afford a wide field for 

 scientific activity. It would be premature to speculate as to how far 

 it will be possible to educe law from what is now chaotic ; but it is 

 clear that the co-operation of many observers will be required to 

 separate the purely local from the true terrestrial changes. The 

 directors of astronomical observatories have peculiar facilities for the 

 study of displacements of the vertical, and it is to be regretted that 

 hitherto most of them have been contented to banish, as far as may 

 be, the troubles caused in their astronomical work by earth-tremors 

 and displacements of the vertical. Fortnightly Review. 



* " Second Report to the British Association on Lunar Disturbances of Gravity,'' 1882. 



Professor Jtdd, in his address at the last annual meeting of the Geological 

 Society, showed that minerals are subject to physiological changes, analogous to 

 those winch take place in plants and animals, though differing in the form of 

 their manifestation and the time they occupy. They have a life-history, he says, 

 "which is in part determined by their original constitution, and in part by the 

 long series of slowly- varying conditions to which they have since been subjected. 

 In spite of the circumstance that their cycles of change have extended over pe- 

 riods measured by millions of years, the nature of their metamorphoses and the 

 processes by which these have been brought about are, in all essential respects, 

 analogous to those which take place in a sequoia or a butterfly." By this, he does 

 not mean that minerals actually live, in the sense in which "living" is popularly 

 understood ; but that, like animals and plants, they go thromrh definite cycles of 

 change, dependent on their environment. Hence the distinction between "or- 

 ganic" or "'living" matter, and "inorganic" or "lifeless "matter, is not funda- 

 mental. 



