TEMPERATURE OBSERVATIONS IN LOCH EARN. 



745 



by Mr Young, Mr Ironside, and Mr M'Ewen. The propeller was towed at as 

 uniform a rate as possible across a water tank, and the deflection corresponding 

 to a definite rate was noted. The calibration was attended with considerable 

 difficulty, as no means were available for towing the propeller through the water 

 at a rate which would remain constant for any length of time. Fig. 3 gives the 

 result of the calibration, and it will be seen that even for currents of 1 cm. per sec. 

 considerable accuracy may be expected. This compares very favourably with the 

 accuracy of the Ekman meters at our disposal, which could not be relied on to record 

 satisfactorily currents of less than 3 cms. per sec. 



The experimental tank was not sufficiently large to admit of the determination 



Fig. 2.— Current-Meter. 



of the directing power of the vanes, but from repeated observation of the instrument 

 in use it is thought that when in proper adjustment the directions registered for a 

 current of the strength of 1 cm. per second were accurate to within ±10 . The 

 wooden floats which have been already referred to were a temporary expedient, and, 

 though heavily varnished, gradually altered in density during their immersion in 

 water. This altered the disposition of density in the instrument, and necessitated 

 constant adjustment of the counterpoises. This defect could easily be remedied in 

 any subsequent instrument. 



Experience, however, showed that the current-meter, with its gymbal bearings 

 and large vanes, was rather unwieldy and sluggish. The adjustment of the vanes 

 for registering vertical currents was a constant difficulty, and the instrument was 

 not always certain in its action. The measurement of the strength of the current 

 by the deflection of a spring propeller was quite successful, and this method would 

 certainly be used if further measurements were to be made. It would be possible to 



