652 MR E. M. WEDDERBURN 
the surface there was often a considerable temperature gradient. The temperature at 
the surface will be seen to be very important, and a first approximation to the period 
may be obtained by assuming there is a sudden discontinuity, above which all the 
water has the surface temperature, and below the bottom temperature. In the fore- 
going calculation for Loch Harn, the surface temperature was taken as 15°7°—if it had 
been taken as 15°5° the calculated period would have been greater by about one 
per cent., which shows how responsive the period of the oscillation is to a small change 
in the density distribution of the loch. 
EXPLANATION OF DIAGRAMS. | 
1. Sketch map of Loch Earn showing position of the observation stations. The nodal lines are those 
determined by Professor CurysTau and the author for the ordinary seiche. Contour lines are drawn for 
50, 100, 200, and 250 feet. ¥ 
2. Boat moored, fore and aft, at Station I., showing sounding drum for thermometers in bow, and wo 
drums for current-meters at stern. 
3. Mr Youne winding up thermometer, showing method of using sounding machine. 
4. Mr Paske reading thermometer. Observe lead marks on the sounding wire. 
5. This is a reproduction of the thermograph record at Tighnadalloch, which was of the ordinar r} 
Richard pattern. It was situated in the open in a very roughly fashioned screen. 
6. This diagram shows temperature-depth diagrams for each station, from noon on 5th August to noon 
on the 6th. The first horizontal line of diagrams refers to Station I., the second to Station II., and so fo th. 
The first vertical column gives curves drawn from observations between noon and 6 p.m, on the bth, The con- 
tinuous curve refers to observations made between noon and 1 p.m., the broken line to observations between 
2-and 3 p.m., and the dotted line to observations between 4 and 5p.m. The second vertical column similarly 
gives curves for observations between 6 p.m. and midnight, for alternate hours; the third column for obserya- 
tions up to 6 a.m. on the 6th, and the fourth column for observations up to noon, The temperature scale in 
each case is horizontal and the depth scale is vertical. 
7. This diagram is drawn in exactly the same way as the preceding one, for the period from noon on 
10th to noon on 11th August, but the curves at each station are only for the hours noon to 1 p.m, and 6 to 
7 p.m. on the 10th, and for midnight to 1 a.m. and 6 to 7 a.m. on the 11th. 
8. This diagram is drawn in the same way as No. 6, save that the first horizontal line refers to obsertil 
tions on the 7th at Station I., the second to observations on the 8th at Station I., the third to observations on — 
the 7th at Station V., and the fourth to observations on the 8th at Station V. 
9. This diagram is drawn in the same manner as the preceding ones, but each curve represents the 
observations between midnight and 1 a.m. at Station III., on successive days from 12th to 23rd August. — 
10. The first 8 curves on this diagram represent he observations at Station V. at six-hour intervals, o on 
24th and 25th August. The ninth curve is from observations at Station I. between 11 p.m. and midnight 
on the 25th. 
11. This diagram shows the variation in depth of isotherms for 10°, 12°, 14°, 16°, and 17°, at Station I 
throughout the month, the time scale being horizontal and the depth one Forieat 
12-14. These diagrams show similarly the variations in level of isotherms for 8°, 10°, 12°, and 14’, 
Stations IL., IIL, and 1V. respectively. 
15. This deeouacn shows the variation in level of isotherms for 10°, 12°, and 14°, at Station V., and ¢ 
the wind pressure throughout the month (measured vertically in kilograms per square metre), drawn by tal 
hourly means from the anemograph records, The line at the top of the diagram indicates the direction 0: 
the wind, Dy 
