428 MR E. M. WEDDERBURN 



very much together. For instance, the temperature of the water brought down by the 

 Oich was 48*3°, and accordingly there is a considerable quantity of water between the 

 isotherms for 48*2° and 48 '4°. Again, the temperature of the water brought down by 

 the Tarff was 487°, and there is also a considerable volume of water between the 

 isotherms for 48 '8° and 48*6°. We may expect, then, in general that the water brought 

 down by rivers will not have any great effect on the water as a whole at its mouth, but, 

 if we look upon the isotherms as membranes, that it will intrude itself between 

 isotherms for temperatures slightly higher and slightly lower than that of the river 

 water. In summer the temperature of the rivers is as a rule higher than the surface 

 temperature of the loch, and so river water will merely lie on the surface. Thus it will 

 not disturb the temperature changes at any great depth. In winter, on the other hand, 

 the temperature of the rivers is as a rule colder than the temperature of the surface 

 water. The water which is brought down will as a consequence sink to the bottom of 

 the loch, and this will tend to make the water at this end of the loch of lower 

 temperature than at any other part of the loch. 



VII. Surface Temperatures. 



There still remain for consideration the temperature changes which occur above 

 the Sprungschicht and near the surface. It was at first hoped that by means of the 

 sunshine receiver some information could be obtained as to radiation into or from the 

 loch. With the weather conditions which obtained during the time observations were 

 made it was impossible to obtain any reliable information in this respect. The 

 mechanism of heating and cooling could not be closely followed. So large a sheet of 

 water was never at rest or free from currents. 



There is no trace of radiation from the loch in any of the records obtained, even on 

 the most likely occasions, so that any information which can be gathered from the 

 observations is of a purely negative character. As to the depth to which the direct 

 effect of the sun's rays is appreciable, there are slight indications in winter that the 

 recorder was sensitive to the sun's rays at a depth of from 12 to 16 feet, but this is 

 really mere conjecture. In August, with the sunshine receiver at a depth of 10 feet 

 there was quite an appreciable indication on the records of the difference between night 

 and day, but the deflection of the galvanometer of the recorder was so slight that the 

 difference between brilliant sunshine and cloud could not be detected. With the sun- 

 shine receiver in air the deflection was nearly 150 times as great as with the receiver at 

 a depth of 1 feet. After a depth of about two feet it was not possible to distinguish 

 between sunshine and cloud. 



Some interesting records of surface temperatures were obtained by means of 

 the platinum thermometers. The surface temperature is seldom in a steady state save 

 occasionally in late autumn or winter, when there is a considerable body of water of 

 uniform temperature near the surface, and when at the same time the temperature of 



