•166 Transactions. — Miscellaneous. 



The rotation of the ethereal corpuscules within the surface of the earth 

 would he so considerably reduced that the force of gravity would be 

 lessened. The corpuscules, whose rotation had been reduced, would react 

 on those at and probably immediately above the surface of the earth. 

 According therefore to the nature of the layer of the earth's crust, whether 

 of greater or less density, so would vary the force of gravity very near the 

 earth's surface. Where these layers were very dense there the force of 

 gravity would be less. In a very hard rocky country the force of gravity 

 would therefore be less than at the surface of the ocean. If a mountain is 

 more dense than the surrounding country the force of gravity on the top 

 of the mountain should be less than on the surronndiug plains. Until the 

 nature of an accelerating force is understood, the principles here sketched 

 cannot be extended with any satisfaction beyond the surface of the earth. 



The following bears directly upon what has just been said : — 



" An immense number of pendulum observations are now being made 

 at the astronomical stations of geodesical surveys in Germany, Eussia, and 

 India, which, when fully published, will throw light more perhaps on the 

 local variations of gravity than on the figure of earth. The observations 

 made at the various stations of the Indian meridian arc bringing to light a 

 physical fact of the very highest importance and interest, namely, that the 

 density of the strata of the earth's crust under and in the vicinity of the 

 Himalayan Mountains is less than that under the plains to the south, the 

 deficiency increasing as the stations of observation approach the Himalayas, 

 and being a maximum when they are situated on the range itself. This 

 accounts for the non-appearance of the large deflections which the Hima- 

 layas, according to Archdeacon Pratt's calculations, ought to produce. The 

 Indian pendulum observations also throw some light on the relative varia- 

 tions of gravity at continental, coast, and island stations, showing that, 

 ivithout a single exception, gravity at the coast stations is greater than at the 

 corresponding continental stations, and greater at island stations than at 

 coast stations." The inference, that because the force of gravity in any 

 locality is less, the density of the earth at that place is less, is one usually 

 made, but it is more credible that mountains are denser than the plains 

 which are made up of detritus from those mountains than that the plains 

 are denser than the mountains."* 



Prof. Darwin made experiments during last year, in which he dis- 

 covered variations in the force of gravity. He has embodied the results of 

 his investigation in a paper which was published in the November number 

 of " Nature" last year. His investigations showed that the force of gravity 

 varied at the very same place, that there was on one or two days a diurnal 

 variation in the force of gravity. 



* See Article " Earth " (figure of) in the Encyclopaedia Britannica, by E. E. Clark. 



