TRANSACTIONS OP THE SECTIONS. 2? 



bles will be produced. A bow-string will cause the same when immersed in water 

 and pulled out of its position of equilibrium. 



The sound of agitated water, which, as a phj'sical phsenomenon, appears to have 

 been overlooked hitherto, is the invariable companion of the bubbles. When the 

 continuous portion of the vein is cut b)"^ the surface underneath no bubbles are pro- 

 duced, and no sound is audible ; but the moment the one appears the other is heard. 

 The sound is in fact almost wholly due to the sudden liberation of the air enclosed 

 in the water ; the ripple of a brook and the roar of the ocean being alike referable to 

 this cause. 



On our Ignorance of the Tides. By the Rev. W. Whewell, D.D., F.R.S. 



The leading features of the general knowledge of the tides, at which we arrive by 

 observations, are the succession of times of high water and low water as we proceed 

 along an extensive coast, or from one part of a large ocean to another ; and the re- 

 lative amount of solar and lunar tides, as shown both by the relative heights of high 

 and low water, and by the amount of the semidiurnal inequality of time. To this 

 may be added the amount of the diurnal inequality, and its incidence ; namely, 

 whether it falls most on high water or low water, on heights or on times. 



Such knowledge we possess with regard to the coasts of Europe, pretty completelj"^, 

 mainly owing to the very general system of simultaneous observations made at Dr. 

 Whewell's suggestion in 1826 ; and also with regard to the Atlantic coast of the 

 United States, our knowledge in that case being entirely supplied by the set of ob- 

 servations made on that coast at the same time. We possess also a tolerably com- 

 plete knowledge of this kind for the eastern coast of Australia, and for some other 

 points of the coast, the diurnal inequality being here peculiar. We know also the 

 general course of the tides on the shores of New Zealand, which may be expressed 

 by saying that the tide-wave comes from the east, and strikes the middle of the 

 eastern shore first. 



And this seems to be the whole amount of the general practical knowledge which 

 we possess on this subject. There appears to be no other extensive coast on which 

 we know the succession of times of high water, still less the semidiurnal and diurnal 

 inequality. On the eastern coast of South America we do not know this with any cer- 

 tainty, though we know that the tides on that coast have curious features ; as for 

 instance, that at the mouth of the Plate river the tides are insensible, and a little 

 further to the south, are some of the greatest in the world. But we do not know 

 on whaCt part of the coast the tide- wave runs south, and on what part north. 



On the west coast of South America we labour under the like ignorance. It appears 

 to be made out by the observations of Capt. FitzRoy and others, that on the southerly 

 part of this coast the tide-wave runs southward, and so round Cape Horn to the 

 eastward, although it might have been expected that the tide, following the moon, 

 would travel westward. But as we proceed northwards along the west coast of Ame- 

 rica, it becomes more difficult to reconcile the separate observations which we have. 

 I have supposed that fiom the isthmus of Panama, the tide-wave diverges northwards 

 and southwards ; but in some of its results this supposition is far from satisfactory. 

 For the northern parts of the N. Pacific, we have Admiral Liitke's observations at 

 the Aleutian islands, &c. ; but these, though correct aa far as they go, only give a 

 partial view. 



Returning to the borders of our knowledge, we find that it ends with the shores of 

 Europe. On the west coast of Africa, we know nothing, so far as I am aware, of 

 the progress of the tide-wave ; whether it travels from south to north, or from north 

 to south ; or where these directions diverge or converge. On the eastern coast of 

 Africa, our ignorance is still more complete ; and though we have some detached ob- 

 servations on the coast of India, we have nothing which gives us a correct view of 

 the progress of the tide. Eastward of India we have remarkable cases of the diurnal 

 inequality (Tonquin, Sincapore), noticed from the earliest to the latest periods of 

 tidal researches, but no connected knowledge ; and as we go further, the tides of 

 the Indian Ocean and of the Pacific become so mingled that we cannot expect to dis- 

 entangle them except by laborious observations. 



As we are thus ignorant of the progress of the shore tides (the littoral tides), so 



