ON SRTSMOLOGICAL INVESTIGATIONS. 



39 



The numbers recorded in successive months were as follow: — 



VI. Observations on Tidal Load at Ryde, Isle of Wight. 



By the kind permission of the Committee of the Koyal Victoria Yacht 

 Club at Eyde I was aUowed to instal an instrument, somewhat similar 

 to the one at Bidston, 1 in one of their. cellars. The room, which is about 

 12 feet below the surface, has a concrete floor. The column to support 

 the instrument is a glazed earthenware drainpipe. At a distance of 

 138 feet from this on the north side, a sea wall forms the face of an 

 outside veranda. With a spring tide the water rises against this to a 

 height of 5 J feet. The same tide 1,50S feet further to the north, which 

 is low-water mark, the depth of the water is about 12 feet. 



From March 4 to April 8 the boom of the pendulum was oriented 

 east-west, so that it recorded tilting of the ground in a north-south 

 direction. It had a period of 15" and 1° turn of the calibrating screw, 

 which gives an angular deflection of l ;/ .9, caused the end of the multi- 

 plying lever to move 11 mm. ; 1 mm. displacement on the photograms 

 is therefore equal to 0".17 of arc. The average ranges of tide at Ryde 

 are from 9 feet to 13 feet. 



A 10-foot tide results in a deflection of 0".85 of arc. At Bidston a 

 10-foot tide gives at a distance of two miles a tilt of 0".2. If the Bid- 

 ston instrument had been installed within 150 feet of the sea the deflec- 

 tions might have been measurably much larger. One inference is that 

 the rocks forming the bed of the Solent are more yielding than the rocks 

 beneath the Irish Sea at Bidston. See Plate I. 



A curious feature in the Byde photograms is the flatness of many 

 of the crests and hollows of the deflections, which seems to indicate 

 that from time to time the water remains high or remains low for 

 several hours. 



On April 8 the instrument was turned through 90°, i.e., the boom 



1 See Brit. Assoc. Report, 1910, p. 49. 



