346 THE ADDRESSES, LECTURES, ETC., OF 



the progress made in that department, which, while dealing chiefly 

 with the preparation of charts showing the depth of water, the 

 direction and force of currents, and the rise of tides near our 

 shores, contains also valuable statistical information regarding the 

 more general questions of the physical conditions of the sea, its 

 temperature at various depths, its flora and fauna, as also the 

 rainfall and the nature and force of prevailing winds. In con- 

 nection with this subject the American Naval Department 

 has taken an important part, under the guidance of Captain 

 Maury and the Agassiz, father and son, whilst in this country the 

 persistent labours of Dr. William B. Carpenter deserve the highest 

 commendation. 



Our knowledge of tidal action has received a most powerful 

 impulse through the invention of a self-recording gauge and tide- 

 predicter, which will form the subject of one of the discourses to 

 be delivered at our present meeting by its principal originator, 

 Sir William Thomson ; when I hope he will furnish us with an 

 explanation of some extraordinary irregularities in tidal records, 

 observed some years ago by Sir John Coode at Portland, and due 

 apparently to atmospheric influence. 



The application of iron and steel in naval construction rendered 

 the use of the compass for some time illusory, but in 1839 Sir 

 George Airy showed how the errors of the compass, due to the 

 influence experienced from the iron of the ship, may be perfectly 

 corrected by magnets and soft iron placed in the neighbourhood 

 of the binnacle, but the great size of the needles in the ordinary 

 compasses rendered the correction of the quadrantal errors 

 practically unattainable. In 1876 Sir William Thomson invented 

 a compass with much smaller needles than those previously used, 

 which allows Sir George Airy's principles to be applied completely. 

 With this compass correctors can be arranged so that the needle 

 shall point accurately in all directions, and these correctors can be 

 adjusted at sea from time to time, so as to eliminate any error 

 which may arise through change in the ship's magnetism or in 

 the magnetism induced by the earth through change of the 

 ship's position. By giving the compass card a long period 

 of free oscillation great steadiness is obtained when the ship 

 is rolling. 



Sir William Thomson has also enriched the art of navigation by 



