1908-9.] Observations with a Current Meter in Loch Ness. 621 
instrument is filled with the balls or shot which are to indicate the direction 
of the current, and the meter is lowered to the desired depth by means of a 
sounding line. One messenger is then sent down which releases the pro- 
peller, and the time at which the messenger reaches the meter is the time at 
which the observation begins. When it is desired to end the observation a 
second messenger is sent down which stops the propeller. The meter is 
then brought to the surface and the number of revolutions which the pro- 
peller has made read on the dials of the meter, the direction of the current 
being ascertained by the position of the balls in the compass box. The 
meter was constructed by the Central Laboratory for the International 
Study of the Sea, Christiania, under the superintendence of Dr Ekman, and 
was carefully calibrated before being sent out, the rate of the current in 
centimeter seconds being given by the formula v — *8 + ‘424 n, where n is the 
number of revolutions of the propeller per minute. The instrument was not 
supposed to be accurate for currents which produced fewer than 5 revs, per 
minute, but in our observations great accuracy was not aimed at and only 
qualitative results were desired. Owing to the conditions under which the 
observations were carried out the instrument could not always be kept in 
perfect adjustment, and for this reason, at least for the slower currents which 
were measured, the above formula is probably not correct. As will be seen 
in the sequel, most of the currents which were measured in Loch Ness were 
slower than 5 revs, per minute ; but as the meter very easily took up the 
direction of the current, the directions were measured with much greater 
accuracy than the velocities of the current. 
It was the exception rather than the rule that the compass balls 
indicated a steady current. The changes of direction were often very 
great during the time occupied by a single observation, and for this reason 
it would have been of great advantage had the balls been distinguishable 
from one another by numbers or otherwise, as then some idea could have 
been obtained of the manner in which the direction of the current varied. 
Such an arrangement was suggested by Dr Ekman, and also by our boat- 
man, Mr Wm. Macdonald, of Fort Augustus. 
It is, of course, necessary to have a fixed point from which to suspend 
the current meter during the observations. The method adopted was that 
used by Helland-Hansen in his current measurements in Norwegian fiords 
in 1906 (. Bergens Museums Aarbog, 1907, No. 15). A buoy was moored at 
the point of observation by two grapnels, to each of which was attached 
a line of a length about twice the depth of water in which the buoy was 
to be moored. The grapnels were put as far apart as the length of the line 
would allow in the direction of the axis of the lake. The lines were then 
