710 REPORT — 1894. 



In some localities it is plainly due to wind, as in the Red Sea, where the 

 eaminer level is some two feet below that of winter, owing to the fact that in 

 summer the wind blows down the whole length of the sea, and drives the 

 water out. 



In many places, as in the great estuary of the Rio de la Plata, the level is 

 constantly varying with the direction of the winds, and the fluctuation due to this 

 cause is greatly in excess of the tidal action. 



In others the cause is not so clear. 



At Sydney, New South Wales, Mr. Russell found that during eleven years the 

 level was constantly falling at alDout an inch a year, but by the last accounts 

 received it was again stationary. 



The variations in the pressure of the atmosphere play an important part in 

 changes of sea level. 



A difference of one inch in the barometer has been shown to be followed by a 

 difference of a foot in the mean level of the sea, and in parts of the world where 

 the mean heis^ht of the barometer varies much with the seasons, and the tidal 

 range is small, this effect is very marked. 



Of any secular change in the level of the sea little is known. This can only 

 be measured by comparison with the land, and it is a question which is the more 

 unstable, the land or the water — -probably the land, as it has been shown that 

 the mass of the land is so trifling, compared with that of the ocean, that it would 

 take a great deal to alter the general mean level of the latter. 



All the points connected with the sea that I have had the honour of bringing 

 before you form part of the daily observation of the marine surveyor when he has 

 the chance ; but I cannot refrain from also mentioning other duties, which ave 

 indeed in the present state of our knowledge and of the practical requirements 

 of navigation the principal points to which he has to pay attention, as it may 

 explain why our knowledge on so many interesting details still remains very 

 imperfect. 



Working as we do in the interests of the vast marine of Great Britain, the 

 paramount necessity of good navigational charts requires that the production of 

 such charts should be our principal aim. 



It is difficult for a landsman and difficult even for a sailor who has never 

 done such work to realise the time that is necessary to make a really complete 

 marine survej% The most important part, the ascertainment of the depth, 

 is done, so to speak, in the dark — that is to say, it is by touch and not \>y 

 sight that we have to find the different elevations and depressions of the bottom 

 of the sea. 



In making a map of the land an isolated rock or hill stands up like a beacon 

 above the surrounding land, and is at once localised and marked, but a similar 

 object under the sea can only be found by patient and long-continued sounding, 

 and may very easily be missed. 



When it is considered that marine surveying has only been seriously under- 

 taken for about 100 years, with a very limited number of vessels, we shall, I 

 think, understand how in the vast area of the waters, taking only those bordering 

 the shores, many unsuspected dangers are yearly discovered. 



Very, very few coasts have been minutely surveyed, and, setting aside for a 

 moment the great changes that take place off shores where sandbanks prevail, 

 I should be sorry to say that even on our own coasts charts are perfect. 



Yearly around Great Britain previously unknown rocks come to light, and if 

 this is the case at home, what are we to think of the condition of charts of less 

 known localities ! 



Our main efforts, therefore, are directed to the improvement of charts for safe 

 navigation, and the time that can be spared to the elucidation of purely scientific 

 problems is limited. 



Nevertheless, the daily work of the surveyor is so intimately connected with 

 these scientific problems that year by year, slowly but surely, we add to the accu- 

 mulation of our knowledge of the sea. 



