of the Fishery Board for Scotland. 
853 
SECTION 0.— PHYSICAL OBSERVATIONS. 
REPORT ON THE PHYSICAL OBSERVATIONS CARRIED ON 
BY THE FISHERY BOARD EOR SCOTLAND IN THE 
FIRTHS OF FORTH AND TAY AND IN THE CLYDE 
SEA AREA. By Hugh Robeut Mill, D.Sc, F.R.S.E. (Plates 
XVI., XVIL) 
The importance to fisheries of a thorough and systematic knowledge of 
the physical changes going on from month to month in the sea being 
fully recognised by the Board, the regular observations which have been 
carried out since 1887 on H.M.S. 'Jackal,' the Fishery cruiser 'Vigilant,' 
and the ' Garland,' were supplemented in 1889 by the inauguration of 
observations at fixed stations. In order that the work done should be 
strictly comparable with that undertaken by the German and Danisli 
Governments on the opposite shores of the North Sea, the Board decided 
to employ instruments of the same description. These were accordingly sup- 
plied and distributed under the direction of Dr John Gibson, who personally 
visited the observers and instructed them in the use of the apparatus. 
The thermometers employed are very serviceable instruments, fitted 
with paper scales inside a protecting glass tube, and graduated to fifths 
of a degree centigrade. They are made by Steger, of Kiel, and enclosed 
for use in wooden cases, the lower part of which is provided with a 
copper box fastened by a spring, and intended to fit loosely, so that 
water can freely enter and be retained around the bulb while the instru- 
ment is being read. The thermometers are admirably adapted for observing 
at sea, being very strong, and, on account of their large wooden cases, 
tliey run little risk of accident. Great care must, however, be taken that 
the copper box slips freely on and ofi" and is clamped firmly by the spring, 
and in actual use a great deal of trouble has been caused by this not being 
the case. In some instances, owing to failure of the spring, th.e copper 
box has been lost, and the observations have in consequence been 
rendered practically useless. More frequently the wooden case, swollen 
by immersion in water, has become tightly wedged, preventing the access 
of water to the bulb. In this event the thermometer is made very 
sluggish in action, requiring from ten to twenty minutes in order to take 
the temperature of the water, and the readings taken after five minutes' 
immersion are thoroughly misleading. Occasionally it has happened that 
the swelling of the wooden case was so great as to split the copper box. 
As each of these drawbacks was brought under notice it was rectified, and 
the observers cautioned as to the risk of any similar occurrence. The 
thermometers were compared by Dr Gibson with a standard instrument, 
and their corrections, which were very small in all cases, were determined. 
The use of the centigrade scale is open to the objection that the 
readings are not directly comparable with, those of the Fahrenheit ther- 
mometers generally used in this country for meteorological work and 
marine research. A table comparing the two scales will be given in this 
Report, and it so happens that the translation of centigrade degrees into 
Fahrenheit is much easier to carry out mentally than the reverse process. 
The rule is, multiply the centigrade temperature by 1-8 and add 32 to 
the result. This is most easily done as follows : — Multiply by 2, subtract 
one-tenth of the result and add 32. For instance, to convert 10° C. to 
degrees Fahrenheit, 10 x 2 = 20, 20 -^ 10 = 2, 20 - 2 = 18, and 18 -f- 32 = 50, 
which, is the answer. 
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