282 APPENDIX. 



the moon upon a body of water, by which any portion is attracted 

 towards her before she is vertically over it, as well as after she has 

 passed to the westward of the meridian of that portion. 



But little attention appears to have been paid to a consideration 

 of the momentum acquired by any great body of water moved from 

 the position it M'ould occupy if undisturbed, and to the consequences 

 of that momentum, when the water returns from a temporary displace- 

 ment. And there seems to be a difficulty in altogether reconciling the 

 statement that " tides are diminished by diffusion,* with the manner 

 in which the great tides of the Northern Atlantic are supposed to 

 be caused — a supposition which is mainly dependent upon theprinciple 

 of " forced vibrations or oscillations. "f 



In consequence of similar ideas, excited by the facts previously 

 mentioned, the following questions were inserted in the Geographical 

 Journal for 1836 : — 



" It may appear presumption in a plain sailor attempting to oiFer 

 an idea or two on the difficult subject of ' Tides ;' yet, with the 

 utmost deference to those who are competent to reason upon the 

 subject, I will venture to ask whether the supposition of Atlantic 

 tides being principally caused by a great tide-wave coming from the 

 Southern Ocean, is not a little difficult to reconcile with the facts that 

 there is very little tide upon the coasts of Brazil, Ascension, and 

 Guinea, and that in the mouth of the great river Plata there is little 

 or no tide .' 



" Can each ocean have its own tides, though affecting, and being 

 affected by the neighbouring waters ? 



" Can the mass of an ocean have a tendency to move westward as 

 well as upward, after and towards the moon as she passes ? If so, 

 after the moon has passed, will not the mass of that ocean have an 

 easterly inclination to regain that equilibrium (with respect to the 

 earth alone) from which the moon disturbed it (sun's action not 

 here considered) ? 



" In regaining its equilibrium, would not its owa momentum carry 

 it too far eastward ; and would not the moon's action be again 

 approaching ? 



" Can one part of an ocean have a M'estward tendency, while another 

 part, which is wider or narrower, from east to west, has an eastward 



• Whewell's Essay, p. 217. 



+ Herscliel's Astronomy, Cab. Cyo. p. 334. 



