486 CURRENTS AND WHALING. 



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 reckoning, and the true place shown by astronomic observa- 

 tions. This method, when practised by good observers, and particu- 

 larly 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 sepa- 

 rately, 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 probably 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 exhibits 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 dis- 



