TRANSACTIONS OF THE SECTIONS. 43 
IL, 
It may be objected that :— 
1. Only a small portion of the earth can be got on one sheet, and there is a 
difficulty in drawing a great circle course between points situated on separate 
sheets. This is true; but by taking some pains in arranging the maps, as has been 
done in this case, and by repeating portions of the earth on two or more sheets, 
matters have been so arranged that scarcely any voyage can be named in which the 
ports of arrival and departure cannot be found, either on the same sheet or on 
opposite sheets, in either of which cases the course can be laid down instantly; and 
even in the rare case of two ports being found on adjacent sheets only, the course 
can be laid down infinitely more easily than it can on a Mercator chart. 
2. It is impossible to find the bearing of one point from another, as can be done 
on the Mercator chart by a compass and a parallel ruler. 
This really is no disadvantage. No one ought to sail along a curved course, and 
no one need care to know any thing about such a course. If this objection be 
seriously urged, it only proves that Mercator’s charts have put false ideas into 
people’s heads, and that other charts are required to replace them, 
Negretti and Zambra’s Patent Recording and Deep-sea Thermometer. 
J i] ap 
By Henry Neererrt. 
This thermometer differs from all other registering or recording thermometers in 
the following important particulars :— 
1, The thermometer contains only mercury without any admixture of alcohol or 
other fluid. 
if It has no indices or springs, and its indications are by the column of mercury 
only, 
3. It can be carried in any position, and cannot possibly he put out of order 
except by actual breakage of the instrument. 
And, lastly, it will indicate and record the exact temperature at any hour of the 
day or night, or the exact temperature at any depth of the sea, irrespective of 
either warm or cold currents or stratum through which the thermometer may 
have to pass in its descent or ascent; this last very special quality renders this 
thermometer superior for deep-sea temperatures to any others ; those which are now 
used in the ‘Challenger’ sounding-expedition are liable to give erroneous indica- 
tions, because their indices may slip and they may become otherwise deranged; and 
under certain conditions of temperature it is not possible by the old thermometers 
to obtain true temperatures at certain depths. Prof. Wyville Thomson says, in 
his work ‘ Depths of the Sea’ :— 
“T ought to mention that in taking the bottom temperature with Six’s thermo- 
meter the instrument simply indicates the lowest temperature to which it has been 
subjected, and not necessarily that of the bottom itself;’ and in confirmation Mr, 
_ Negretti quoted a report to the Admiralty from Captain G. 8. Nares, of H.M.8, 
‘Challenger,’ dated Melbourne, March 25, 1874 :— 
“ Ata short distance from the pack, the surface-water rose to 82° F., but at. a depth 
of 40 fathoms we always found the temperature to be 29°; this continued to 300 
fathoms, the depth in which most of the icebergs float, after which there is a stratum 
of slightly warmer water of 33° or 34°. As the thermometers had to pass through 
these two belts of water before reaching the bottom, the indices registered those tem-_ 
peratures, and it was impossible to obtain the exact temperature of the bottom whilst 
near the ice, but the observations made in lower latitudes show that it is about 31°, 
More exact results could not have been obtained even had Mr. Siemens’s apparatus 
been on board.” 
The thermometer described, the author believes, will be found free from the 
defects of the thermometers now in use in the ‘Challenger’ and other sounding- 
expeditions. 
he bulb of the thermometer is protected so as to resist the pressure of the ocean, 
which varies according to depth, that of three thousand fathoms hea shout three 
