402 



Messrs. Carpenter, Jeffreys, and Thomson [Nov. 18, 



Apparatus it will be desirable to provide for the proposed Expedition for 

 Marine Researches, beg leave to lay before the Council the following 

 Report : — 



" The chief subjects of Physical Enquiry which presented themselves as 

 interesting on their own account, or in relation to the existence of Life at 

 great depths, were as follows : — 



" (1) The Temperature both at the bottom and at various depths be- 

 tween that and the surface. 



" (2) The nature and amount of the dissolved Gases. 



" (3) The amount of Organic matter contained in the water, and the 

 nature and amount of the Inorganic salts. 



tc (4) The amount of Light to be found at great depths. 



"Among these subjects the Committee thought it desirable to confine 

 themselves in the first instance to such as had previously to some extent 

 been taken in hand, or could pretty certainly be carried out. 



" The determination of Temperatures has hitherto rested chiefly upon 

 the registration of minimum Thermometers. It is obvious that the tem- 

 perature registered by minimum thermometers sunk to the bottom of the 

 sea, even if their registration were unaffected by the pressure, would only 

 give the lowest temperature reached somewhere between top and bottom, 

 not necessarily at the bottom itself. The temperatures at various depths 

 might indeed, provided they nowhere increased on going deeper, be deter- 

 mined by a series of minimum thermometers placed at different distances 

 along the line, though this would involve considerable difficulties. Still, 

 the liability of the index to slip, and the probability that the indication of 

 the thermometers would be affected by the great pressure to which they 

 were exposed, rendered it very desirable to control their indications by an 

 independent method. 



" Two plans were proposed for this purpose, one by Sir Charles Wheat- 

 stone, and one by Mr. Siemens. Both plans involved the employment of 

 a voltaic current, excited by a battery on deck ; and required a cable for the 

 conveyance of insulated wires. The former plan depended upon the action 

 of an immersed Breguet's thermometer, which by an electro-mechanical 

 arrangement was read by an indicating instrument placed on deck. The 

 latter plan made the indication of temperature depend on the existence of 

 a thermal variation in the electric resistance of a conducting wire. It 

 rested on the equalization of the derived currents in two perfectly similar 

 partial circuits, containing each a copper wire running the whole length of 

 the cable, the sea, and a resistance-coil of fine platinum wire ; the coil in 

 the one circuit being immersed in the sea at the end of the cable, and that 

 in the other being immersed in a vessel on deck, containing water the tem- 

 perature of which could be regulated by the addition of hot or cold water, 

 and determined by an ordinary thermometer. 



"The instruments required in Sir Charles Wheatstone's plan were more 

 expensive, and would take longer to construct; and besides, the Com- 



