69 
1907-8.] The Body-Temperature of Fishes, etc. 
essentially of two parts — the thermometer itself, and the frame on which 
it is mounted, devised to invert the thermometer at any given depth, the 
temperature being registered at the moment of inversion. When the 
instrument has been sunk to the desired depth, a weight — the “ messenger ” 
— ingeniously made of iron or lead in two pieces, so that it can be placed 
on the line at any point, is allowed to run down, and this, when it comes 
in contact with the frame, liberates a spring-catch which holds the top- 
heavy thermometer in position, and allows it to make half a revolution. 
The bulb of the thermometer is protected from pressure by being enclosed 
in an outer glass case partially filled with mercury. 
In operation, the depth of the water was first ascertained with a deep- 
sea lead, the line being marked at intervals of 10 fathoms. The line was 
then hauled in, the lead detached and replaced by the thermometer frame, 
which was run down to within a fathom of the bottom. The “ messenger ” 
was then slipped on to the line and sent down, so as to liberate the spring 
catch and allow the thermometer to invert itself. On bringing the 
thermometer up, the temperature was read off and recorded. Readings 
as just described were taken near the bottom, and at 10-fathom intervals 
between that and the surface, twice on most occasions during the “ slack.” 
I was surprised to find that the temperature of the sea was practically 
uniform throughout, and was inclined to doubt the accuracy of my 
thermometer, since I had expected that the water would be warmer near the 
surface than deeper down ; but on referring to a paper by JEL N. Dickson 
in the Reports of the Scottish Fishery Board for 1893 I came upon the 
explanation. While taking soundings, temperature and other observations 
on H.M.S. Jackal in the North Sea- Atlantic channel between the Orkney 
and Shetland Islands, Dickson found that at stations in the North Sea 
east of this channel, where the water was comparatively still, the tempera- 
ture fell steadily from the surface downwards, and at a depth of 50 
fathoms there was a difference of several degrees (13° # 6 F. or 7 0, 6 C. in 
one instance) ; but at stations in the tideway off Sumburgh Head where 
the current runs at the rate of 7 knots, “the mixing of the water is 
so complete that the temperature does not vary 0°*1 C. from surface 
to bottom in a depth of 50 fathoms.” For my work this was a very 
fortunate circumstance, since no heat could be gained or lost by the 
fish while being brought from the bottom, as might conceivably have 
been the case if the temperature near the surface had differed by several 
degrees from that deeper down. 
An accurate Centigrade thermometer, graduated in fifths and readable 
to tenths, was employed for taking the body-temperature of the fish. 
