68 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Temperature of Fishes. 
While spending a holiday in the Orkney Islands during the month of 
September of this year, cod-fishing was being carried on by the local boats 
in the Pentland Firth, and it occurred to me that this would offer an 
excellent opportunity of making some observations on the body-temperature 
of the fish caught. I accordingly obtained permission to join a fishing- 
smack, and proceeded to sea provided with the necessary requirements. 
Fishing in the Pentland Firth is done by the “ hand-line,” since, on 
account of the rocky character of the sea-bottom, neither the trawl nor 
“ long-lines ” can be employed. The rate of the current with spring tides 
is from 8 to 10 knots (9 to 11 \ miles per hour), and with neap tides from 
4 to 5 knots, and it is only for about an hour at the turn of the tide that 
fishing can be engaged in. The flood tide runs south-east for about six 
hours, the ebb tide north-west for six hours, and for an interval of about 
fifteen minutes with neap tides and less with spring tides, between the 
end of the flood and the beginning of the ebb tide, little or no current 
is detectable. This is known locally as the “slack of the flood,” and 
the corresponding interval between ebb and flood as the “ slack of 
the ebb.” 
Our usual fishing-ground lay about the middle of the Firth, from one to 
three miles west of the island of Swona. Most frequently we fished at 
the flood “slack.” The smack was hove to towards the end of the 
flood tide ; she drifted or “ carried ” slowly south-east, then remained 
practically stationary from ten to fifteen minutes, and then began to drift 
in the opposite direction with the ebb, at an ever-increasing rate, the lines 
being kept out until the current became too rapid. The whole fishing 
period did not cover much more than one hour. The crew consisted of five 
men, each working one “ hand-line ” with a six-pound leaden sinker and two 
hooks baited with limpets and lug (Arenicola). The depth of water was 
usually a little over 50 fathoms, and, the cod being a ground-fish, the 
baits were run to the bottom. 
My object was to compare the temperature of the fish with that of 
the water in which they habitually lived, and it was therefore necessary 
that I should be able to ascertain accurately the temperature of the sea 
at or near the bottom. For this purpose I employed Negretti and Zambra’s 
patent deep-sea reversing thermometer, mounted on a frame of the Scottish 
Marine Station pattern. A detailed description of this instrument will 
be found in the Challenger Reports (1876), vol. i., part 1, pp. 88-95, but 
it has been considerably modified and improved since that date. It consists 
