218 



BATHYMETRICAL SURVEY OF 



north-west end, owing to the north-west winds prevailing during the 

 time the Lake Survey was on the loch. For instance, on July 19 the 

 temperature of the surface north-west of Rudh' Aird an Anail was 

 53-9 at 3 p.m., and off Ardlair it was 54-0 at 4 p.m., whilst at 

 3.15 p.m. it was 55*3 to the south-east of Fhasaigh. 



Five serial observations were taken on July 19 and 21, as given in 

 the following table : 



Below the surface the fall in temperature was slow down to about 

 50 feet, when the fall became very rapid down to 150 feet, and then 

 slow again to the bottom. Though these are the characteristics of the 

 three series taken on the 21st, that taken on the 19th to the south of 

 Eilean Ruairid Mor in the Slattadale basin does not agree with the 

 others. In this case there was a rapid fall from 20 to 100 feet, and 

 then a slight rise in temperature to 150 feet, and then a slow fall again 

 to 200 feet. 



The series taken to the north of Eilean Ruairid Mor on the 21st is 

 interesting on account of the decided inversion at 25 feet. Though 

 these inversions of temperature have occasionally been observed, they 

 are by no means common. In this case it was noticed that the tempera- 

 ture fell from 53'9 at the surface to 53'7 at 10 feet, and to 53'3 at 15 

 feet, and then rose to 53'5 at 25 feet, and then fell again steadily below 

 this depth. The series down to 25 feet was repeated with the results 

 shown in the second column under this head, which proved that the 

 inversion, though small, was real and not due to the instrument. 



