96 THE FRESH-WATER LOCHS OF SCOTLAND 
frequently used for observing deep-water temperatures ; but a maximum 
and minimum thermometer can only be used where it is known that 
there is a continuous rise or fall in temperature from the top to the 
bottom, for the thermometer only gives the maximum and minimum 
temperatures to which it has been subjected while being lowered and 
raised, and this is not necessarily the temperature at the depth to which 
it has been lowered. The reversing thermometer is, however, not open 
to this objection, as it registers the temperature at the time it is made 
to turn upside down, irrespective of the temperature of the water 
through which it passes while being raised or lowered. 
During the Loch Ness observations use was made of platinum 
resistance thermometers in conjunction with a Callendar recorder. 
Some observations with resistance thermometers had previously been 
made in America by Mr Warren, who used a telephone to measure 
the changes in resistance of a platinum thermometer, and one of his 
instruments was used by the Survey. Dr F. M. Exner^ also used 
ingenious electrical resistance thermometers in the Wolfg-ans^see 
with considerable success, but no observations on a large scale had 
previously been attempted by electrical means." The object of the 
electrical installation was to obtain a continuous record of tempera- 
tures at any depth. The arrangement used was designed for the 
Lake Survey by the Cambridge Scientific Instrument Co., Ltd., 
and is referred to in my paper on lake temperatures.^ It was not 
altogether satisfactory, but the experience gained in working with 
it would probably enable the observers to design an apparatus which 
would work well ; and this method of observation, giving, as it does, 
continuous records of the temperature, has great advantages over 
observations made with mercury thermometers. 
Effect of Configuration and Geographical Position 
ON THE Temperature of a Lake 
It is difficult to enumerate all the factors which play a part in 
determining what shall be the temperature of the waters of a lake, 
but these factors may be discussed under the following heads : — 
(1) the depth of the lake and the area of its surface, (2) its altitude, 
1 " Messungen der taglichen Temperaturschwankungen in verschiedenen 
Tiefen des Wolfgangsees," Sitzungsber. Akad. Wiss. TVieii, Bd. cix., Abt. ii.a, 1900. 
"Tiber eigentiimliche Temperaturschwankungen von eintagiger Periode im 
Wolfgangsee," ihid., Bd. cxvii., Abt. ii.a, 1908. 
2 A thermo-electric junction was used to measure temperatures in the Lake of 
Geneva in 1836 by MM. Bequerel and Breschet (Bibl. Univ. Geneve, t. vii, p. 173, 
1837). This is probably the first attempt to measure lake temperatures by 
electrical means. 
3 See Trans. Roy. Soc. Edm., vol. xlv. p. 410, 
