On the Distribution of Temperature, etc. 313 



down the lake. At Tarbet there is a deep rift in the mountains 

 separating Loch Lomond from Loch Long, which gives access 

 to the westerly winds to this part of the lake. On the whole, 

 the geographical position of the lake tends to neutralise the 

 effect of the prevailing winds. 



Extended temperature observations were made on the 

 following days: i8th August, 5th and 22nd September, I5th 

 October, and i4th November. On the i8th August observations 

 made only in the Tarbet basin, and only down to a depth 

 of 30 fathoms. On the 5th September observations were made 

 in the Luss basin, at four stations in the Tarbet basin, and at 

 one station in the Ardlui basin. On the 22nd September 

 observations were made in the Luss basin, and at two stations 

 in the Tarbet basin. On the I5th October observations were 

 made at the same stations as on 5th September, omitting 

 Culness; and on I4th November observations were made in 

 the Luss basin and at Inversnaid. 



The observations were made with an improved form of 

 protected six's thermometer, having a millimetre scale on the 

 stem and a Fahrenheit scale on slips at the side. The average 

 length of a degree Fahrenheit was three millimetres, and all 

 the thermometers had been carefully and repeatedly compared 

 with each other, and with a Kew corrected standard. The 

 temperatures given are all in terms of the Kew standard. As 

 a rule, the same thermometer has been sent to the same depth. 

 Further, the same sounding-line was used on all occasions. 



The results are collected in tables, and in some cases they 

 are represented graphically by curves. 



If we represent the distribution of temperature graphically 1 



by a curve, having depths measured along the horizontal line 



of abscissae and temperatures along the ordinates. the winter 



distribution will be represented by a straight line parallel to 



the line of abscissae, such as A. As the spring advances and 



the meridian altitude of the sun daily increases, the temperature 



<>f the surface rises rapidly. The heat received at the surface 



luring this season, propagated downwards, chiefly by 



conduction, which, in water, is a comparatively slow process, 



1 See i-i.y. i. p. 314. 



