(| G28) 
XXVI.—Temperature Observations in Loch Earn. With a further Contribution 
to the Hydrodynamical Theory of the Temperature Seiche. By E. M. 
Wedderburn, W.S. 
(Read March 4, 1912. MS. received March 18, 1912. Issued separately December 14, 1912.) 
INTRODUCTORY. 
There are a number of gaps which exist in our knowledge of the temperature 
changes which occur in fresh-water lakes. The broad lines on which the changes occur 
are fairly well known, but on almost every point there is a lack of detailed knowledge, 
and every investigation shows new problems requiring attack. One of the most 
interesting of these problems is the causation of the temperature seiche, and the effect of 
varying meteorological conditions. The problem is a difficult one, as the factors to be 
taken into consideration are so numerous, and the data from which to form conclusions 
are difficult to procure. We must first obtain an accurate knowledge of the changes 
which are occurring in the body of water under consideration—not only at one 
point but at all points, and this necessitates observations at frequent intervals of time, 
at numerous depths, made from several points on the surface of the loch. As yet there 
are no satisfactory self-recording instruments by means of which we can record the 
temperature of water at a considerable depth below the surface, and recourse must be 
had to the reading of mercury thermometers. 
PLAN OF THE INVESTIGATION. 
In order to obtain a fairly complete record of the temperature changes occurring 
over a period of time, observations on a somewhat ambitious scale were undertaken 
in Loch Harn during August 1911, the cost of these being defrayed by a grant from 
the Sir John Jackson ‘Tait Memorial Fund of the University of Edinburgh and a sub- 
sidiary grant from the Earl of Moray Endowment of the University ; Loch Earn was 
chosen as the scene of operations for the same reasons as weighed with Professor 
CurystaL in his seiche investigations, viz. the uniformity of its basin, its con- 
venient size, and its accessibility. Another very cogent reason lay in the fact that 
the ordinary seiches had previously been so carefully investigated by CurystaL, and 
it was hoped that the loch would be found as well tuned for the temperature seiche as 
for the ordinary seiche. 
A map of the loch will be found in the Transactions of the Society, Vol. XLLI., 
TRANS. ROY. SOC. EDIN., VOL. XLVIII. PART III. (NO. 26). 92 : 
