TEMPERATURE OF THE ISEA (J J 



whicli it protects will, therefore, soon indicate an 

 equilibrium of temperatui'e between itself and the 

 surrounding water. 



The temperature of the deeper waters is not the 

 same as that of the superficial mass. It is therefore 

 necessary to employ instruments, so constructed as to 

 keep a record of the extreme temperatures through 

 which they are passed. To effect this, P^ron en- 

 closed the instrument in a tube made of a substance 

 that was a bad conductor of heat. This apparatus, 

 being immersed for a sufficiently long time, at lengtli 

 acquired the temperature of the water that surrounded 

 it, and being quickly withdrawn, there was no time 

 for the heat to escape before the indication was read off*. 



Bunten has attained the same end, by inventing what 

 he calls the " Thermometer Plunger." The instru- 

 ment is put into a tube closed by a valve, which opens 

 from the exterior to the interior; thus allowing the 

 water of the sea to enter, but preventing it from re- 

 turning when the apparatus is withdrawn. The ther- 

 mometer, therefore, is brought to the surface sur- 

 rounded with sea- water; but it is easy to see that we 

 cannot be sure of the depth from which the water is 

 taken, as in the case of Peron's instrument. Finally, 

 the thermometer is not protected from the pressure 

 of the water. Bunten's Plunger, therefore, is not 

 available for deep thermometric soundings. 



