590 
ME. J. PEESTWICH ON SUBMAEINE TEMPEEATUEES. 
Owing to the want of a reliable self-registering thermometer, three plans were 
resorted to by the earlier observers to ascertain the temperature of the sea at depths 
below the surface. The first and more common plan was to bring up water from a 
determined depth in sufficient quantity and with sufficient speed to prevent any material 
change of temperature, and then to try it with an ordinary thermometer, although some- 
times the thermometer was suspended in and descended with the water-bucket. In the 
second place, the thermometer was surrounded with a non-conducting substance, and 
left down a length of time sufficient to acquire the temperature of the surrounding 
medium and then brought rapidly to the surface. In the third place, the temperature 
was taken by means of mud or silt brought up from the bottom. On a few occasions 
metallic thermometers have been tried, but not with satisfactory results. These several 
plans continued in use from time to time up to a comparatively late period, until 
gradually superseded by self-registering thermometers. 
As the error due to pressure in the use of the latter instrument has now been deter- 
mined with sufficient accuracy, most of the older observations can readily be subjected 
to correction. Such correction has been applied to all the observations that have been 
used in constructing the Sections, Plates 66-68 ; but, as in the Tables themselves the 
original readings are given without correction, in order to obtain in any case, with a few 
exceptions named, an approximately true reading, the correction given at p. 612 must be 
applied. Where, from the use of proper precautions, the original readings are presumed 
to be correct, they are distinguished by being placed between brackets in the Sections. 
§ II. Historical Narrative of Deep-sea Observations , 1749-1868. 
In this chapter I have enumerated in chronological order the various voyages on 
which I have found any record of deep-sea temperatures — stating generally the course 
gone over, the number of observations made, the depths attained, the methods employed. 
At the end the correction for the errors attendant on these methods is determined. The 
particulars of the observations taken on each voyage will be found in the Tables by 
reference to Column VIII., under which is given the name of the officer in command, 
or of the scientific observer accompanying the expedition. The conclusions formed by 
them on these data are reserved to the next chapter. 
It was about the middle of the last century that the subject of deep-sea temperatures 
first began to attract attention. In 1749 Captain Ellis, on the occasion of a voyage 
to the north-west coast of Africa, made two experiments at depths of 3900 and 5346 feet 
in lat. 25° 13' N.*, with an instrument devised by Dr. Hales, and described by him in a 
paper to the Royal Societyf. It consisted of a bucket about the size of an ordinary 
pail, with valves at top and bottom, which remained open as the apparatus descended, 
and closed as it ascended. He obtained in both cases readings of 53°; and he rightly 
attributed this uniformity to the greater depth of water through which, in the deeper 
experiment, the instrument had to be hauled, and which caused a larger gain of heat. 
* Phil. Trans, for 1751-1752, vol. xlvii. p. 214. f Ibid, p, 213. 
