TEMPERATURE OBSERVATIONS IN LOCH EARN. 



765 



mounting, but during the remainder of the series the variation is much more 

 irregular. The irregularities are due to slight winds, which seem to have such a 

 marked effect in changing the form of the oscillation, as has been noticed in previous 

 investigations. The slow mounting during the calm gives a very accurate means of 

 determining the true period of the oscillations. The rate of increase of phase is 

 about 20° per group, and hence a better approximation to the true period of the 

 uninodal seiche is 20 x (1 + 20/360) hours = 211 hours. 



The curves for the two stations are very much alike, which is a strong corrobora- 

 tion of the standing-wave theory. 



Harmonic Analysis: 



II' Isothermal. 19/3 August 24-29. 



Period: 20 Hours 



STATION NO. I : 



Station No. IT, ■ 



Mean Depth 



OF II' ISOTHERHAL 



28fo h 



hrlPLITUDE 



OF UNINODAL SEICHE 



28 d O h 



r\l1PLITUDE 



OF BINOOAL SEICHE 



Phase ' 



of uninodal seiche 



Phase 



OF BINODAL SEICHE 



Fig. 17. 



3. Amplitude of the Binodal Seiche. — In the case of the binodal seiche there is 

 no strong maximum, but the whole is less regular than the curve of the amplitude 

 of the uninodal seiche, and suggests that the former is more easily disturbed than 

 the latter. 



The difference between the curves for Stations 1 and 2 is much more apparent, 

 as would be expected. A similar calculation to that given for the uninodal amplitude 

 on the assumption of approximately plane isothermal surfaces through the binode 

 gives the factor 1*28. The actual ratio is about 1*41, indicating that the gradient of 

 the isotherm increases towards the end of the loch. The change of wave type 

 discussed on page 756 gives a probable explanation of this, but at first sight it is 

 rather remarkable that the gradient of the isotherms should be so different in the 

 cases of the uninodal and binodal seiches. The wave-length of the binodal seiche 



TRANS. ROY. SOC. EDIN., VOL. L, PART IV (NO. 191 105 



