V. Note on an Error in the Method of Determining the 

 Mean Depth of the Ocean from the Velocity of Seismic 

 Sea-waves. By Charles Davison, Sc.D., F.G.S., King 

 EdivaraVs High School, Birmingham* . 



THE data we possess for determining the mean velocity V 

 of sea-waves are the distance A and the time of transit T. 

 From these we obtain 



Y=A/T. 



We have, from hydrodynamics, the further equation 



V-^foH), 



in the case when the sea is of considerable but uniform depth 

 H along the path traversed by the wave. 



If the depth of the sea is variable, it is generally assumed 

 that the quantity H given by the equation 



^H)=A/T 



is the mean depth of the ocean along the path of the wave. 

 But when the mean depth along the same path can also be 

 obtained from soundings, it is found to be greater than that 

 which is given by the above formula. 



In the case of the Krakatoa sea- waves of August 26-30, 

 1883, a large number of very careful calculations were made 

 by Capt. W. J. L. Wharton, F.R.S.f; and his results, so far 

 as they concern the subject of the present paper, are given in 

 the following Table. The stations marked with an asterisk 

 are those at which the records were obtained by automatic 

 gauges. In the second column the figures denote the mean 

 depth of the sea calculated from the formula, and in the last 

 column the mean depth obtained from known soundings. 



* Communicated by the Author. 



t " On the Seismic Sea- waves caused by the Eruption of Krakatoa, 

 August 26th and 27th, 1883.'' ' The Eruption of Krakatoa and Subse- 

 quent Phenomena,' pp. 89-150. 



Phil. Mag. S. 5. Vol. 43. No. 260. Jan. 1897. D 



