THE 



GEOLOGICAL MAGAZINE, 



NEW SERIES. DECADE V. VOL. VI. 



No. IV.— APRIL, 1909. 



OI?,IC3-I3Sr.A.ILi ^A.E,TICXuES. 



I. — Seculak Eakth-Cheep. 



By Professor E. II. L. Schwaez, A.R.C.S., F.G.S., Ehodes University College, 



Grahamstown. 



DR. J. It. SUTTON has recently read a most important paper to the 

 Eoyal Society of South Africa on the diurnal variation of level 

 at Kimberley. The paper gave the preliminary results of observations 

 made during the course of three years upon the variation of the level 

 of the ground as recorded by a large horizontal pendulum of a special 

 design made for the author by the Cambridge Instrument Company. 

 It appeared from the results that the movements in the surface of the 

 ground, which set up corresponding movements in the pendulum, were 

 very great. The maximum westerly elongation of the extremity of 

 the pendulum occurred about 5.30 a.m., the maximum easterly about 

 4.15 p.m., the medium positions a little before 11 a.m. and 9.30 p.m. 

 Geometrically these movements may be represented on the hypothesis 

 that the hemisphere facing the sun bulges out, forming a sort of 

 meniscus to the geosphere. The rise and fall of the surface of the 

 ground which such a supposition would postulate is enormous, and 

 the very magnitude has led Dr. Sutton to hesitate in giving the figures. 

 There can, however, be very little doubt that some rise and fall in the 

 earth's surface is occasioned by the sun's gravitational pull, although 

 the present figures may have to be lessened by taking into consideration 

 other causes which contribute to the disturbance of the pendulum. 



The subject is not a new one ; Professor Milne, in his Bakerian 

 lecture, referred to experiments he had carried out at Shide, Isle of 

 Wight, in which it was proved that the earth's surface bulged on 

 a sunny day and was depressed on a cloudy or rainy day ; the cause 

 for this was the different rates of transpiration in the leaves of the 

 trees, grass, and so forth, which led to the accumulation of water in 

 the soil on a cloudy day sufficient to weigh down the earth. Such 

 elevations and depressions, however, leave no permanent distortion, 

 but when the earth is day by day pulled out towards the sun, this 

 must in the course of geological periods cause the ridges in the earth's 

 crust to creep westwards. 



DECADE V. — VOL. VI. NO. IV. 10 



