CURKENT OBSERVATIONS. 121 



the stream was found to be flowing, the value from noon to noon 

 of the observed current being shewn by the numbers beside them. 

 The direction and value of these currents are of necessity only an 

 approximation, being the course and distance between the position 

 of the ship as found by observation and of that estimated by 

 account. It will be readily understood then that accuracy is 

 dependent upon the correctness of observation for latitude, longi- 

 tude, and compass error on the one hand, and upon good steering 

 and exactness in logging on the other. Inaccuracies due to errors 

 in observation are as a rule small, and the same may be said in 

 regard to the steering of a fast modern steamer, but this is not 

 the case in respect to logging. Hand logs and patent logs alike 

 are not to be relied upon in estimating accurately the speed at 

 which a fast steamer is travelling or the distance she has travelled. 

 The hand log or patent log influenced by the disturbed water in a 

 steamer's wake will denote a rate of progress under or in excess 

 of her actual rate, in the one condition of the vessel's trim, although 

 it may have recorded the actual speed through the water in 

 another condition of trim. The accuracy, to sum up, of a log 

 will therefore depend upon the approximation of a vessel's trim 

 to one particular condition, and no workable amount of stray line 

 will altogether eradicate this error. In the case of a patent log 

 moreover, the slip of the rotator will be found to vary according 

 to the speed of the vessel, and as the mechanism, from the effect 

 of friction, will probably after a time offer slightly reduced resist- 

 ance to the action of the rotator, a corresponding variation in the 

 rate of the machine will result. It is far from my intention to 

 condemn the use of the hand or patent log generally. In the daily 

 navigation of sailing vessels, and of all steamers of low, or com- 

 paratively low power, whose speeds are easily affected by conditions 

 of wind and weather, the assistance that may be gained by their 

 use, is in my opinion invaluable, as it is also in full powered 

 steamers at times, notably when on account of fog the speed main- 

 tained is not uniform, or in intricate navigation, when the course 

 has to be altered frequently upon the completion of short distances. 



