of Edinburgh , Session 1884 - 85 . 165 
including the cases considered in Table V. The former table shows 
that the upper half of the water has nearly the whole difference of 
the temperature to account for, and it is probable that quite a small 
layer is heated above or cooled below the temperature of the great 
bulk cf the water. 
The figures already given may be considered as describing the 
variation of temperature with the seasons at the various parts of the 
Firth ; the variation of temperature with position at the same time 
of year must also be considered. The temperatures observed in the 
various long water-sampling trips are given in Table VII. They 
show how, in the 55 miles between Alloa and the Isle of May, the 
temperature is never at any one time uniform, and this is very dis- 
tinctly brought out by the curves of these figures. With the ex- 
ception of the first expedition (in September), all of these were 
made in the water-winter, that is at a time when the radiation from 
the land and sea at night was greater than that to them by day, 
and when as a consequence the shallower and more land-locked 
waters were colder than those deeper and nearer the sea. The 
curves have all an upward slope towards the sea in consequence, 
with the exception of that for September and that for April. The 
latter is a nearly straight line, showing that at present (20th April 
1885) the lower reaches of the Firth are at an almost uniform tem- 
perature of 43° (see Plate VII. fig. 1). Collecting all the avail- 
able observations of surface temperature, and taking the mean of 
those in the four divisions of the Firth for each half-yearly period, 
the following table (VIII.) is arrived at : — 
Table VIII. 
1 . 
2. 
3. 
4. 
Summer (June-September) . 
57-0 
55‘3 
49-2 
48-0 
Winter (October-J anuary ) . 
42*3 
437 
47-3 
48-4 
The diagram (Plate VII. fig. 2) shows that in summer the tempera- 
ture falls pretty rapidly from Alloa to Inchgarvie, and more slowly 
right out to sea. In winter this state of matters is exactly reversed, 
the temperature rising continuously from the river seawards. The 
