I860.] On tie Translation of Waves of Water. 267 



once formed and the original cause withdrawn, or as they may be 

 termed free, obey the same laws, and are subject to the same pecu- 

 liarities. 



4. The undulation upon a smooth sheet of water from a school 

 boy's pebble ; the ocean wave thrown up by the wind ; the gush of water 

 from a destroyed dam or suddenly- withdrawn barrier ; the swell from 

 a steamer's paddle ; and the great free tide-wave which, twice in the 

 twenty -four hours is poured into all estuaries and rivers through the 

 inequality of the attraction of the heavenly bodies : — all these waves 

 so diiferent in origin, size, and formation, are subject to the same 

 series of laws, which have been, to a certain extent, investigated. 



5. It should first be remarked that the progress of a wave is not 

 the progress of the particles of which it is composed. A traveller, 

 upon visiting the sea-shore for the first time, might be led to suppose 

 that each wave was bringing with it the mass of water of which it 

 was originally composed, and depositing it upon the shore. A little 

 closer observation would, however, soon convince him of his mistake, 

 as he would perceive that a piece of drift wood or of foam, would 

 maintain the same mean distance from the beach, although several 

 successive waves lifted it upon their crests, and deposited it in their 

 succeeding hollows. 



6. The same law may be shewn to hold with the tidal wave. In 

 the accompanying tide table (with a copy of which, if thought useful, 

 I shall be happy to furnish the Society annually) — the time of high 

 water at Calcutta, or of the passage of the crest of the tidal wave 

 at that place, is predicted for every day throughout the year. In 

 the lower part of the sheet, the distances of places from Calcutta 

 along the river are given in geographical miles, and against each, 

 under the column of " correction for high water," is the interval of 

 time which the crest of the wave occupies in travelling that distance. 

 With these data it will be seen that the tidal wave of the Hooghly 

 has a mean speed between Saugor and Calcutta of about 20^ geogra- 

 phical or 24 British miles per hour — while the speed of the water 

 perhaps never exceeds eight, and is frequently as low as 2 miles 

 per hour — without any corresponding variation in the rate of trans- 

 lation of the wave. The position, moreover, of the junction of the 

 salt water of the ocean, with the fresh water of the river stream, is 



2 n 2 



