1890-91.] Dr John Murray on the Temperature of Lochs. 139 
On the Temperature of the Salt and Fresh Water Lochs 
of the West of Scotland, at Different Depths and 
Seasons, during* the Years 1887 and 1888. By John 
Murray, LL.D., Ph.D. 
(Read February 16, 1891.) 
The temperature observations recorded in this communication 
were all taken from the yacht “Medusa,” except those in Loch 
Morar, which were made from a small rowing-boat, but the same 
instruments and the same methods were used as in the other lochs. 
All observations beneath the surface were made by means of 
Messrs Negretti & Zambra’s reversing thermometer in the Scottish 
frame. The readings are published as they were observed, except 
that the instrumental correction is applied. The readings may, as a 
rule, he taken as exact to one-tenth of a degree when the sea was 
smooth, and when the temperature of water and air had a range 
less than six degrees. Experiments have shown that if a ther- 
mometer be reversed in water at 40° *0, and then brought to the 
temperature of 46° *0, it would change its indication slightly, and 
would read 40° *1. At first sight it would appear sufficient to sub- 
tract 0°T from the reading for each 6° of excess of air temperature 
over that registered by the instrument, and to add similarly in case 
the air temperature should be lower. This has not been done, 
because it was believed that, in summer at least, the cooling caused 
by evaporation from the wet instrument would reduce its temper- 
ature very considerably, and probably enough to make no correction 
necessary. 
When it was possible to do so temperature was observed at very 
short intervals of depth, wherever there was a sudden change. For 
this reason, and in order to make it easy to compare conditions at 
any one depth, the somewhat diffuse plan of recording the readings 
was adopted. 
Air temperature was observed by means of the sling thermometer. 
The hour mentioned is in each case that at which the observation 
was commenced. 
The weather being “ bright 55 or “ dull ” means that the sky was 
not much clouded and the sun shining, or that it was overcast. The 
sea was always smooth, except where the contrary is noted. In 
