TEMPERATURE OBSERVATIONS IN LOCH EARN. 755 



The most interesting current observations are those made early on the morning 

 of 14th August. The first indication of a current was obtained from the manner in 

 which the wire to which a thermometer was attached bellied out. Observations 

 with the current-meter were at once commenced, and strong easterly currents which 

 were practically horizontal were found at depths down to 10 metres. Observations 

 below that depth were also made, and showed either slow currents or none at all. 

 The currents were well marked for about four hours, after which they seemed 

 suddenly to cease. 



During this time the loch was dead calm, and a surface current could hardly be 

 detected. About 20 h. on the evening of the same day strong currents were also 

 found from the east near the surface, and again at this hour there was a sudden fall 

 in the isotherms. 



From the observations it may be concluded that at the windward end of a 

 loch the currents produced by even moderately strong winds have not a large 

 vertical component, but that at the lee end there is quite a considerable vertical 

 component. We may also conclude that near the end of a loch, when owing to the 

 presence of a temperature seiche or other causes the isotherms are rising or falling 

 rapidly, the vertical component of the currents so produced may be considerable, 

 and that rapid movements of the isotherms produce eddies or vortices. In general, 

 however, it must be said that the vertical component of loch currents is not con- 

 siderable. 



Observations with Mercury Thermometers. 



A large number of observations was made with ordinary reversing thermometers 

 at each of the two anchored boats, and on various occasions observations were made 

 from boats anchored at intermediate points. The observations made at the beginning 

 of the month were of a preliminary character to determine the temperature distribu- 

 tion and the nature of the changes in progress, but it was found that to be of any 

 service observations would require to be made simultaneously for a longer period than 

 12 hours. Accordingly, from 10 h. on 13th August until 21 h. on 15th August observa- 

 tions were carried on at each of the two boats. Two thermometers were employed 

 on each boat, and about 20 observations were made each hour. 



From the observations so obtained curves were drawn showing the time variation 

 in temperature at various depths ; from this curve a second curve showing the 

 oscillations in the level of various isotherms. Figs. 8 and 9 show the isotherms 

 for 10°, 12°, and 14° at each of the stations. 



Prior to the commencement of the observations on 11th and 12th August there 

 were variable winds and calms. On the morning of the 1 3th it was calm ; a 

 moderate westerly wind sprang up about 11 h. 30 m. and lasted until 22 h. 30 m., after 

 which there were calms or light winds until 22 h. on the 14th. A steady east wind 

 then sprang up which fell away about 9 h. on the 15th, and during the remainder of 

 the series there was a calm. 



