758 DR E. M. WEDDERBURN AND MR A. W. YOUNG ON 



a well-earned holiday in preparation for the strenuous week which was to follow. 

 The thermograph, which had been out of gear, was, however, set to work again at 

 10 metres on the evening of the 23rd, and at 19 h. recorded a temperature at that depth 

 of about 127° C. The temperature at this depth at 19 h. on 22nd August was 8'6° C. 

 It is seen from examination of fig. 10 that the mean level of the 127° isotherm was 

 about 10 metres, so that apparently the isotherms at 19 h. on the 23rd were approxi- 

 mately in their normal positions. 



The thermograph record for the night 23rd to 24th August (fig. 13) shows that the 

 temperature at 10 metres did not vary more than 17° C, so that apparently no large 

 oscillation was in progress. In the first 24 hours after observations were commenced 

 on 24th August the temperature at 10 metres varied 2"5° C, and as even in the 

 record obtained by means of the thermograph 1'3° of the variation took place after 

 7 h. 50 m. on the morning of the 24th, it would appear that the observations were begun 

 practically at the commencement of a series of oscillations. 



— i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 i i 



20h 2lh. 22h. 23h. 24h. I h. 2 h. 3 h. 4h. 5 h. 6h. 7 h. 8h 9h. lOh. Ilh. IZh. I3h. 



Fig. 13.— Thermograph Record at 10 metres— 23rd-24th August 1913. 



It is remarkable that this should be so, for one would have expected that the 

 oscillation would have commenced immediately the isotherms began to swing back 

 when the wind moderated. Apparently, however, this was not so, and the only 

 explanation which can be suggested is that when the wind moderated a solitary wave 

 was started at the Lochearnhead end which, after being reflected at the east end of 

 the loch, gradually resolved itself into a standing oscillation. The experimental 

 investigations made by Mr Wedderburn in 1905 support this. 



Calculation of the Period of the Temperature Seiche. 



The period of a temperature seiche can be approximated to by the method de- 

 scribed in the communication on the temperature seiche, Trans. Roy. Soc. Edin., 

 vol. xlvii, part iv, p. 635, without the labour of finding the seiche equations for 

 the loch. 



If T is the period of the temperature seiche in August 1913 and t the period 



in 1911, 



m_ , area of surface of discontinuity in 1913 (h of normal curve 1911)* 

 area of surface of discontinuity in 1911 (h of normal curve 1913)* 



The average distribution of temperature on 28th August 1913 at the anchored 



boat was as follows : — 



metres 15-0° C. 16 metres 10-0° C. 



5 „ 146° C. 18 „ 9-4° C. 



10 „ 14-0* C. 20 „ 9-0° C. 



12 „ 13-5° C. 25 „ 81° C, 



14 „ 11-1° C. 



