176 



REPORT 1897. 



observations to determine the mean velocity of propagation, which is that 

 of the greatest movements. 



Shock 3. — Movement in Europe was extremely small, and no record 

 was obtained at Nicolaiew. Possibly the smallness of the diagram, which 

 began 'little by little,' may have rendered it difficult to make accurate 

 measurements on the time scale. 



The general result of the examination of data which have led to the 

 determination of velocities which appear to be either too high or too 

 low, is to find that such data are either imperfect or capable of another 

 interpretation. 



The doubtful cases are placed in circles, and to these, based upon a 

 long experience in observing earthquake velocities over ranges up to about 

 1,000 kms., I should be inclined to add Nos. 33, 39, 40, 43, and 42. 



If, therefore, we exclude the computations the accuracy of which is doubt- 

 ful, the general results towards which the continuation of the observations on 

 the propagation of earth-waves over ranges of varying length point is 

 approximately indicated in the following table : — 



VII. Diurnal Waves. By John Milne, F.R.S., F.G.S. 

 Observations made on the Tennis Ground at Shide Hill House. Installation V. 



On September 5, 1896, the horizontal pendulum which had been in 

 use at Carisbrooke Castle was brought to Shide, where it was installed on 

 a slate slab resting on an upended earthenware drain-pipe, sunk some 

 inches in the ground, covered by a jointer's tent standing in the middle of a 

 tennis ground. The chief object of this installation was to study the diurnal 

 wave, as shown by the movements of a pendulum so placed that for ten or 

 twenty yards, at least, on all sides of it the surface conditions were fairly 

 similar. The tennis ground is in the middle of a small paddock which 

 slopes towards the west. On the eastern side, at a distance of forty 

 yards, is the building in which instrument T was installed, beyond which 

 the ground quickly rises to Pan Down. The sun, rising on this side, reached 

 the tent over the top of some high trees at about 9 a.m., throwing the 

 shadow of the tent towards the N.W. At about 4 P.M. this shadow, after 

 travelling through N. to the N.E. was lost, as the sun sank behind Mount 

 Joy on the west. 



The bromide film was run at a rate of about 3^ inches in twenty-four 

 hours, which was sufficiently rapid to give an easily measurable diagram of 

 the daily movement of the pendulum, the boom of which pointed from its 

 pedestal towards the south. 



On September 13 a heavy tarpaulin (30 x 30 ft.) was spread over the 

 grass, immediately up to the tent on its west side. On October 13 this 



