5 o THE WATER 



A form of insulating thermometer which may be 

 of use in some cases is an instrument of the ordinary 

 form, the bulb of which is surrounded by a thick mass of 

 a badly conducting material india-rubber, for instance. 

 Such a thermometer will take some hours to come to 

 the temperature of the surrounding water, and will 

 take a similar time to lose this temperature on hauling 

 up into the air. If the thermometer be hung just 

 clear of the bottom from, for instance, a lightship, 

 and be hauled up at intervals of some hours for read- 

 ing, it is possible that the records will give some 

 indication of the changes below. Under certain 

 conditions, where there is a very small daily range, the 

 readings may be of real value. 



Methods of Using Water-Bottles, etc. 



All modern instruments are made for use on wire 

 and not on hemp rope, and in most cases only for a 

 stranded flexible wire of a diameter of from 2 to 4 

 millimetres. The single wire is not now generally used, 

 on account of its great liability to kink and break. 

 The stranded wire is much safer, but of course offers 

 more resistance to the water. The writer has used 

 successfully a wire rope of about 2-2 millimetres 

 diameter with a breaking strain of 400 pounds. 



through the points plotted is suspect, and should be re- 

 peated. This method will also show any " critical " horizon 

 at which the change of temperature is sudden ; round this 

 horizon more numerous observations should be taken at, say, 

 50 fathoms interval. At each observation mark the number 

 of the thermometer used ; this will soon show up an unreliable 

 instrument. These thermometers are made for Admiralty 

 use with an extra large scale, which admits of very close 

 readings, and is to be recommended. ED. 



