458 CURRENTS AND WHALING. 



those who have used this instrument extensively must be, that it is 

 liable to many objections, and that in particular if the current be 

 beneath the surface, or, for want of a better term, may be denominated 

 submarine, no result can be obtained by its use. If not perfect, how- 

 ever, the current log was at least a useful indicator; and its regular 

 use, which was ordered to take place whenever the state of the sea 

 would permit, served to keep the subject of currents continually before 

 us. It is unnecessary to recount the number of the experiments that 

 were performed ; suffice it to say, that they were made both by day 

 and by night, and were persevered in until the record of them became 

 an almost daily portion of our journals ; and the interest in them was 

 extended from the officers, until they became a subject of inquiry even 

 among the crews. 



Upon the chart that exhibits the tracks of the squadron when united, 

 and of the vessels when separate, the direction and force of the upper 

 currents is indicated. The results thus expressed were obtained by a 

 comparison of the position assigned to the vessels by the dead reckon- 

 ing, and the true place shown by astronomic observations. This 

 method, when practised by good observers, and particularly when 

 furnished with chronometers of such excellence as can now be obtained, 

 is in my opinion that which is liable to the fewest objections. Still it 

 is to be desired that the allowances in the dead reckoning for lee-way, 

 the heave of the sea, steerage, &c, should be founded on principles so 

 certain as to admit them to be applied separately, and that less was 

 left to the mere judgment of the navigator. The use of steam in 

 navigation, and the introduction of improvements in the log, will pro- 

 bably bring about this desirable result. 



In order to attain greater certainty, every calculation on which the 

 rate and direction of a current was founded, has been made anew since 

 the return of the Expedition ; and it is trusted that the chart now ex- 

 hibits a full and correct representation of the action which influenced 

 the position of the vessels, freed in a great measure from the causes of 

 uncertainty of which I have spoken above. 



On the same chart are represented the courses of the winds, and 

 the isothermal lines for every five degrees of the thermometer, from 

 30° to 95°. The zones lying between these lines are coloured in tints 

 varying from cold to warm, in order that at a single glance the curves 

 may be conspicuous. By simple inspection it will be seen how close 

 is the connexion between the position of these lines and the figure of 

 the zones they enclose, with the flow of the streams of which I am 

 about to treat. It will at least be obvious that the distribution of the 

 temperature at the surface of the ocean is affected by causes very 



