1903.] on Some Problems and Methods of Oceanic Research. 371 



before the end of the voyage, all the temperatures above referred to 

 were taken with the Millar-Casella maximum arid minimum protected 

 thermometer. It is owing to the use of this instrument that the 

 temperature work of the Challenger during little over three years 

 is comparable 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 re- 

 stricted 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 Mediter- 

 ranean, 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* and other Scottish 

 Lakes, as well as that of the Gulf of Guinea which I carried out on 

 board the Buccaneer f in the early part of the year 1886. It differs 

 from the original Challenger pattern in being longer and having 

 two scales. The one scale carries either Celsius' or Fahrenheit's 

 degrees on enamel slips fixed to the vulcanite backing of the ther- 

 mometer and close alongside the stem. The other is a scale of 

 millimetres, etched on the stem itself. This is the real scale of the 

 instrument, and the value of its divisions is determined by careful 

 comparison with a standard thermometer. At every observation 

 both scales are read and the readings recorded, and the one always 

 corrects the other in the case of a misreading. In my instruments 

 the length of one Fahrenheit's degree was from 2*5 to 3 millimetres, 

 which enables the temperature of very deep water to be determined 

 with great exactness. An exploring ship should always carry some 

 thermometers reversing by messenger to test cases where from the 

 indications of the maximum and minimum thermometer the law of 

 decrease of temperature with increase of depth seems to be departed 

 from. 



Samples of intermediate water were collected at depths of 800, 

 400, 300, 200, 100, 50 and 25 fathoms, and a separate operation was 

 required for each depth. At a full station this necessitated the 

 liandling of 1875 fathoms of line. This service was performed 

 without the loss of any material whatever. 



* Proceedings of Eoyal Society, Edinburgh, 1885, vol. xiii., p. 403. 

 t ' The Scottish Geographical Magazine,' April and May, 1888. 



