328 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
THE MILLER-CASELLA DEEP-SEA THERMOMETER. 
Plate XXII shows this thennometer in the copper case used for deep-sea work; 
also partially dismounted to show the form of coustructiou. The magnet seen 
between the two instruments is used to adjust the indices. 
The following’ description is from Sigsbee’s Deep-sea Sounding and Dredging, 
page 108 : 
A glass tube bent in the form of U is fastened to the vulcanite frame, and to the latter are 
secured white glass plates containing the graduated scales. Each limb of the tube terminates in a 
bulb. A column of mercury occupies the bend and a iiart of the capillary tube of each limb. 
The large bulb and its corresponding limb above the mercury are wholly filled with a mixture of 
creosote and^vater; the opposite limb above the mercury is partially filled with the same mixture, 
the remaining sj^ace therein being occupied by comj)ressed air. In the mixture, on each side, is 
a steel index having a horsehair tied around it near the upper extremity. The ends of the elastic 
horsehair, being held in a i)endant position by the inner walls of the tube, exert enough pressure 
to oppose a frictional resistance to a movement of the index in elevation or deiiression. As thus 
described, the instrument is a self-registering maximum and minimum thermometer for ordinary 
use. The indications are given by the expansion and contraction of the creosote and water mixture 
in the large full bulb. 
The instrument is set by bringing the lower end of the indices in contact with the mercury l>y 
means of a magnet provided for the purpose. Then, when the instrument is submitted to a higher 
temperature, the exjiansion of the mixture in the large bulb dej>resses the column of mercury on that 
side and correspondingly elevates it on the other side. A decrease of temperature contracts the 
mixture in the large bulb, .and by the elastic force of the compressed air in the smaller bulb a 
transference of the column of mercury takes place iu precisely the reverse manner to th.at which 
occurs on .a rising temperature. Thus the mercury rises in the left limb for a lower and in the right 
limb for a bigher temperature. The greater the change of temperature the higher the point reached 
iu the resjiective limbs; hence the scale on the loft is graduated from the top downward, and that on 
the right from the bottom upward. The rising of the mercury iu either limb carries with it the 
index of that limb, .and on the retreat of the mercury the index rem.ains at the highest point attained. 
The bottom of the index, being the part which has been in contact with the mercury, gives the jtoiut 
at which to take the reading. 
The large bulb of this thermometer is now protected from pressure by a glass 
shield which surrounds it; the space between the shield and bulb is nearly filled witli 
alcohol, which acts as a transmitting medium for temperature, performing the same 
function as the mercury in the shield of the ISTegretti & Zambra tliermometer. The 
shield above mentioned has added much to the value of tlie instrument, as it has 
practically eliminated errors arising from varying pressures. 
This thermometer has been considered the standard for deep-sea work, and when 
several were to be sent down to great depths on the same line it was unrivaled until the 
present improvements in the methods of capsizing the ISlegretti & Zambra thermometers 
were introduced. It is not as sensitive as the Negretti & Zambra, but under the above 
conditions a delay of a few minutes is not of great importance. 
The movable indices are a fruitful source of annoyance and vexatious delay. An 
index may, without apparent cause, absolutely refuse to move in the tube; coaxing 
with the magnet is followed by lightly tajiping the frame in the hand or swinging it 
rapidly about the head, and if this fails more vigorous tapping is apt to follow with 
vai’ious active measures, none of which tend to improve the general condition of the 
instrument. The indices are also liable to move if the instrument is subjected to rough 
treatment, although this is not of fre»]uent occurrence with careful handling. 
Most of the minor casualties to which the instrument is liable are apparent to the 
eye and are readily adjusted. 
