in the Twenty Years before 1895 45 



in amount with all the temperature work which has been 



done by other ships in the thirty years since her date. The 



reversing thermometer is an indispensable instrument for 



observations in isolated depths, and for series of temperatures 



in the very restricted localities where the great law of the 



decrease of temperature with increase of depth does not hold. 



The total extent of these localities is less than one-tenth of that 



of the whole ocean. They cover the two polar areas and the 



neighbouring waters which are affected by the presence of ice. 



In lower latitudes they include only the so-called enclosed 



basins, the largest of which is the Mediterranean, and in these 



the law holds rigorously down to a definite depth. The whole 



of the open ocean lying between the parallels of 50 N. and 



50 S. can be thoroughly investigated with the protected 



maximum and minimum thermometer, and if hemp line be 



used, seven or eight of them, as experience showed, can be 



safely risked in each operation. The actual pattern to be 



used is the one with which I supplied the late Mr Casella on 



the return of the "Challenger"; and with it I have made 



all my later temperature investigations, notably the thermal 



survey of Loch Lomond 1 and other Scottish Lakes, as well 



as that of the Gulf of Guinea which I carried out on board 



the " Buccaneer" 2 in the early part of the year 1886. It differs 



from tin- original "Challenger" pattern in being longer and 



having two scales. The one scale carries either Celsius' or 



! ahrrnhrit 's degrees on enamel slips fixed to the vulcanite 



backing of the thermometer and close alongside the stem. 



"th<T is a scale of millimetres, etched on the stem itself. 



1 In- i^ the real scale of the instrument, and the value <1 it- 



determined by careful comparison with a standard 



mometer. At every observation both scales are read 



the readings recorded, and the one always corrects the 



r in the GEM Of ft misreading. In my instruments the 1. 



dirrnhrit's degree was from 2-5 to 3 millimetres. \\hu h 

 enables the temperature .,f very deep watei t<> 1>< d t< i mined 

 with great c\ I, An exploring ship sh,,ni,i .ilways carry 



1 Proceedings of K ;trgk, 1885, Vol. xm. p. 403. 



The Scottish Geograph nine, April and May, 1888. 



