1908-9.] Observations with a Current Meter in Loch Ness. 619 
XXXVIII. — Observations with a Current Meter in Loch Ness. 
By E. M. Wedderburn, W.S., and W. Watson, M.A., B.Sc.* 
(MS. received July 5, 1909. Read July 5, 1909.) 
One of the authors having made an experimental investigation on the 
currents produced in a trough of water by a blast of air driven along the 
surface of the water, j* it was desired to test the correctness of his deductions 
by actual observations in a large lake. Loch Ness was chosen on account of 
its length and uniformity of basin, as it was thought that the length and 
narrowness of the loch would lead to clearly defined currents being set up in 
the lake. The sequel showed, as in the case of observations on seiches, that 
it would have been better to confine attention to a smaller lake, for a two- 
fold reason, (1) because in a large lake the difficulties of observations are 
much greater than in a small lake during stormy weather, and in very deep 
lakes the difficulties in the way of obtaining a fixed point from which 
to use the current meter are formidable, and (2) because it would seem 
from a few observations made in Loch Garry (Ness Basin) that currents are 
more defined and more regular in small than in great lakes. 
Various current meters have been designed, and after inquiry it was 
decided that the one best suited for observation in lakes was the instrument 
designed by Dr Ekman and described by him in Publications de Circonstance 
No. 24, and the choice was justified by the satisfactory way in which the 
instrument worked under adverse conditions. Fig. 1 gives a photograph of 
the instrument. The current is measured by the number of revolutions of 
a very light screw propeller, which is kept directed against the current by a 
vane set at right angles to the propeller. By an ingenious arrangement, at 
every thirty-three revolutions of the propeller a small metal ball is allowed 
to drop into a cup in the centre of a compass needle, after which the ball runs 
down a groove on the north leg of the needle into the compass box, which is 
rigidly attached to the meter. The compass box is divided into 36 divisions, 
* The cost of the current meter and the necessary gear with which the observations 
described were carried out was partly defrayed by a grant from the Moray Bequest of the 
University of Edinburgh. The cost of carrying on the observations was partly borne by a 
grant from the Carnegie Trustees. We have also to acknowledge indebtedness to Professor 
D’Arcy Thompson for advice, and for supplying a small but strong sounding machine for use 
with the current meter, and to Mr J. Davidson, Superintendent of the Caledonian Canal, for 
the use of a buoy and anchor and for assistance in preparing the necessary gear. 
t E. M. Wedderburn, “An Experimental Investigation of the Temperature Changes 
occurring in Fresh-water Lochs,” Proc. Roy. Soc. Edin ., xxviii. p. 2. 
