930 
Proceedings of the Royal Soeiety 
The observations included two complete tides, and it was 
observed that when the water began to enter at 6 p.m. the bottom 
temperature began to rise from 54° until at 9 p,m. it reached 55°. 
The surface temperature was meanwhile falling. The night was 
cloudy, and from 9 p.m. to 6 a.m. the readings of the surface and 
bottom thermometers were practically the same. At 6 a.m. the tide 
began to enter, and the bottom temperature fell slowly from 55° 
to 54° *6. The whole of the next day was dull and cloudy, and the 
temperatures of air and of water varied little. The tidal effect observed 
was somewhat puzzling, for the temperature of the water of the Firth 
was known by previous observations to be several degrees lower 
than that in the quarry, and not to vary appreciably with the hour. 
In order to get additional evidence, the 25th and 26th June were 
selected for another series of observations. The 25th was cloudy 
and cool, the air temperature being altogether below the average 
for the two days, the night was pretty clear, and the 26th turned 
out bright and warm. As I had more assistance than on the former 
occasion, observations were made every half hour at three stations 
in different parts of the quarry — one near the mouth where the 
depth at low water is 5 fathoms, the second was the Ark in 6 
fathoms, the third a buoy in the north-west corner in 8 fathoms. 
The means of the observed temperatures are as follows : — 
For 30 Hours Daylight. For 6 Hours Darkness. 
Air, ... 59-5 54 '9 
{ Entrance, . 56 ’61 
Ark, . . 56 T 7 55 ’52 
N.W. corner, 56 ‘52 
{ Entrance, . 55 '51 55*65 
Ark, . . 55*74 55*97 
N.W. corner, 54*92 55*82 
For 36 Hours. 
58*6 
56*05 
55*55 
55*64 
55*24 
The course of the temperature curves at the Ark on those two 
days is shown in Plate XIV., where the tidal effect is plainly notice- 
able. The observations embraced three complete tides. When the 
water began to enter at noon, there was a steady rise of bottom 
temperature, and when it entered at 1 a.m. next day there was as 
distinct a fall; while on its coming in at 1.30 p.m. a very abrupt 
rise of almost a degree was observed at each of the stations. The 
curve of surface temperature followed that of air temperature in the 
main, as on the previous day. 
