40 A Retrospect of Oceanography 



way than by observing the apparent rise of temperature as 

 indicated by the maximum index when exposed to pressure 

 in an hydraulic receiver. The portion of this which was due 

 to rise of temperature by the compression in the receiver 

 was certainly not applicable to a thermometer passing rapidly 

 through the limitless waters of the ocean, and that part of it 

 which was due to actual compression of the thermometer 

 could only be applicable in the proportion of the exposed 

 portion of the minimum limb above the index to that of the 

 whole stem up to the maximum index, or to less than one- 

 tenth part. But the tenth part of the pressure correction 

 was always less than the probable error of reading an instrument. 

 The truth of this conclusion was demonstrated by experiments 

 made in the hydraulic apparatus on board. It was fitted 

 on the main deck; and in the tropical regions, where the 

 experiments were made, a mass of water equal to that in the 

 experimental receiver did not vary by a fraction of a tenth 

 of a degree Centigrade during the whole period of the experi- 

 ments. I mention this, not only to show that the change 

 of apparent temperature indicated by the maximum index 

 of the thermometer under compression was produced by action 

 in the receiver, and was in no way due to changes of temperature 

 in the atmosphere, but also to call attention to the very favour- 

 able temperature conditions offered by a ship in tropical 

 regions for carrying out physical experiments. The choice of 

 such a laboratory would usually be dismissed without examina- 

 tion, while a little experience would reverse the decision. 



While in the Antarctic regions, the impossibility of deter- 

 mining the temperature of the water with the thermometers 

 available gave me cause for much thought, and it was not 

 until we had left the icy regions that a method of adapting 

 them to the occasion occurred to me. As similar conditions 

 might be found to obtain in the waters near the Falkland 

 islands, which we should pass through on the way home, 

 I caused some special Six's unprotected thermometers to be 

 sent out to me. My intention was, if the temperature gradient 

 was found to be inverted, to open the extremity of one of these 

 thermometers, and send it down open. It would then be 



