1874.] Physics. 
277 
Messrs. Negretti and Zambra have recently communicated to the Royal 
Society the description of a new Deep-sea Thermometer. For the purpose of 
ascertaining the temperature of the sea at various depths, and on the bottom 
itself, a peculiar thermometer was, and is, used, having its bulb protected by 
an outer bulb or casing, in order that its indications may not 
be vitiated by the pressure of the water at various depths, 
that pressure being about 1 ton per square inch to every 
800 fathoms. This thermometer, as regards the protection 
of the bulb and its non-liability to be affected by pressure, 
is all that can ‘e desired; but unfortunately the only ther- 
mometer available for the purpose of registering temperature 
and bringing those indications to the surface is that which 
is commonly known as the Six’s thermometer—an in- 
strument acting by means of alcohol and mercury, and having 
movable indices with delicate springs of human hair tied 
to them. This form of instrument registers both max- 
imum and minimum temperatures, and as an ordinary 
out-door thermometer it is very useful; but it is unsatis- 
factory for scientific purposes, and for the obje@ which it is 
now used it leaves much to be desired. Thus the alcohol 
and mercury are liable to get mixed in travelling, or even by 
merely holding the instrument in a horizontal position; the 
indices also are liable either to slip if too free, or to stick if 
too tight. A sudden jerk or concussion will also cause the 
instrument to give erroneous readings, by lowering the in- 
dices if the blow be downwards, or by raising them if the 
blow be upwards. Besides these drawbacks, the Six’s ther- 
mometer causes the observer additional anxiety on the score 
of inaccuracy ; for, although we get a minimum temperature, 
we are by no means sure of the point where this minimum 
lies. Messrs. Negretti and Zambra have constructed an in- 
strument on a plan different from that of any other self- 
registering thermometers. Its construction is most novel, 
and may be said to overthrow our previous ideas of handling 
delicate instruments, inasmuch as its indications are only 
given by upsetting the instrument. Having said this much, 
it will not be very difficult to guess the action of the thermo- 
meter; for it is by upsetting or throwing out the mercury 
from the indicating column into a reservoir, at a particular 
moment and in a particular spot, that we obtain a correct 
reading of the temperature at that moment and in that spot. 
The instrument has a protected bulb thermometer, like a 
syphon with parallel legs, all in one piece, and having a con- 
tinuous communication, as in the annexed figure. The scale 
of this thermometer is pivotted on a centre, and being at- 
tached in a perpendicular position to a simple apparatus 
(presently described), is lowered to any depth that may be 
desired. In its descent the thermometer aéts as an ordinary 
instrument, the mercury rising or falling according to the 
temperature of the stratum through which it passes; but so 
soon as the descent ceases, and a reverse motion is given to 
the line, so as to pull the thermometer to the surface, the 
instrument turns once on its centre, first bulb uppermost, and 
afterwards bulb downwards. This causesthe mercury, which 
was in the left-hand column, first to pass into the dilated 
syphon bend at the top, and thence into the right-hand tube, 
where it remains, indicating on a graduated scale the exact 
‘temperature at the time it was turned over. The woodcut 
shows the position of the mercury after the instrument has 
been thus turned on its centre. A is the bulb; B the outer 
LONDON 
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coating or protecting cylinder; c is the space of rarefied air, which is reduced 
if the outer casing be compressed ; p is a small glass plug, on the principle of 
VOL. Iv. (N.S.) 
2N 
