0 
TirE VOYAGE OF H.M.S. CHALLENGER 
A sunmuiry of tlie results is given in that paper at page 42, where it is shown 
that at a depth of 2500 fathoms, or nearly 3 miles, the mean correction of all the 
thermometers examined is only 0°-27 Fahr., the largest correction of any one of these 
thermometers beino; 0°'41 Fahr. 
'I’he observations of deep-sea temperatures strictly as observed, no correction being 
thus shown to be needed, are published in the Challenger Reports, together with 
the siune temperatures represented by curves on 258 plates.^ The curves 
are drawn, libera manu, through the observations, which are fully detailed at 
the toj) of each plate, allowance being thus made for such errors of observation as 
10*, 5'", 1*, &c. d'he figures adopted in constructing the accompanying maps of deep-sea 
tem|)crature are taken directly from the curves. In dealing with the other observations 
employed in this discussion, the observations as read are alone employed, any correction 
for pressure on the bulbs of the thermometers being in no case allowed for. As regards 
the imjxjrtant series of observations made by Commander Belknap, U.S.S. “Tuscarora,” 
it is stated in his Report, p. 18, what corrections were applied to the thermometers for 
depths of 100, 300, 500, and 700 fathoms, but no further explanation is given. An 
examination, however, of the observations themselves at all depths as printed makes it 
.sufficiently jtlain that Caj)tain Davis’ correction of half a degree Fahr. for each mile 
of depth had been aj)plied throughout. Before, therefore, entering the temperature 
ob.servations of the “Tuscarora” on the maps, they were increased by the amount by 
which they had manifestly been diminished, before publication, by the application of 
(’ajttain Davi.s’ rule. It was interesting to note that when the “ Tuscarora’s ” course 
wa.H in the vicinity of the course of the Challenger, “ Egeria,” &c., the additions made to 
the published readings brought them into accordance with the readings of these other ships. 
;V.s this discu.ssion deals only with depths at which the temperature is virtually 
uninfluenced by .season, no depths less than 100 fathoms are examined. The 
tcmpeniturc maps which accompany this Report are for depths of 100 fathoms, and 
then, in succession, for each additional 100 fathoms down to 1000, then for 1500, for 
2200 fathoms and another for bottom temj)eratures. It is plain that in this discussion 
MO tomjKiratures of the surface of the sea are admissible except good mean annual 
tcmjKiraturca of the surface, it being these and these alone that rule deep-sea 
tcmi»cratures. Hence it is impo.ssiblc to overestimate the value of Lieut. Baillie’s map 
xhowing the mc<'in annual distribution of the temperature of the surface. 
In order to arrive at a correct knowledge of the mean temperature of the ocean 
••onsidcred as a whole at each of the <lei)ths selected, all the temperatures at each depth 
were avcniged, exclinling the temperatures which are from so-called “ closed areas.” 
The mean tcmj)crature thus arrived at is entered on each map, and in drawing the 
-ithcrmal lines, all temjKiratures above this mean are represented by red lines, and 
' See A nit, So. I, footnote, p. 3. 
