170 Lieut. Spratt on the Influence of Temperature 



It will be seen by this table that the temperatures of the 

 upper zones are frequently two or three degrees higher near the 

 coast than the average temperature of the corresponding depth 

 at the distance of five or six miles, indicating apparently a 

 terrestrial influence. 



The average temperature of the air during summer in the 

 iEgean is 86° ; and the above observations show that the sea 

 within the littoral zone, viz. under two fathoms, is from 73° 

 to 78°. In the three lower regions the temperature decreases 

 rapidly ; so that in the fourth region, at the depth of 35 fa- 

 thoms, the temperature of the sea is 20° lower than in the first 

 region, being about 60° or 62°. In the sixth region the 

 temperature is about its minimum, viz. 55° or 56°, only 4- 

 or 5 degrees less than in the fourth region. I have not been 

 able to prove the temperature at a lower depth than 230 

 fathoms, at which it stood 55±°, as in the seventh region. 



It is necessary for me to mention the difficulties I experi- 

 enced in making the observations at great depths correctly, 

 the labours of several hours having been often lost through 

 the motion of the vessel ; the twisting and jerking of the line 

 whilst hauling it up again, by which means the steel bar of the 

 Six's thermometer was shaken down the tube; thus showing 

 a higher temperature than what the contents of the dredge 

 showed when brought up with it. I finally found the plan 

 of testing its temperature by the mud brought up more cer- 

 tain than that of lowering the thermometer, when the contents 

 of the dredge was of a sufficient quantity to retain the lower 

 temperature, and the sea-bottom a soft mud, as it almost 

 always is in depths above 100 fathoms. Under that depth, 

 and in corally, gravelly and sandy bottoms, the thermometer 

 must be lowered. 



It may thus be doubted whether the mud when brought up 

 from such a depth really showed the temperature of the bot- 

 tom ; the question being, whether it is not lower than the mud 

 indicated, owing to a gain of temperature by passing through 

 regions of a higher grade. I however have no reason to sup- 

 pose that the temperature is lower than 55° at any depth under 

 300 fathoms, having often tested the contents of a dredge after 

 it had been some time standing on the deck of the vessel in a 

 tub of water of the surface temperature. The certainty of 

 there being a temperature as low as 55-}° in the seventh and 

 eighth region of depth, is sufficient for the remarks 1 shall 

 make upon its influence upon the distribution of marine fauna. 



I will now endeavour to show, by analysing Prof. Forbes's 

 report, that the key to the solution of that remarkable distri- 

 bution of marine fauna into regions of depth is the decrease 



