DEEP-SEA EXPLORATION. 
329 
KIDDER’S THERMOMETER COMPARISONS AND CORRECTIONS. 
Suro-eon J. II. Kidder, U. S. K., had charge of the thermometers of the United 
States hdsh Commission from 1S83 to lS8d, during whicli time he compared every 
instrument before it was issued for service. Since then they have l)een corrected 
by the United States AYeather Bureau. Kidder’s methods and appliances were 
sul'ticiently simi)le and effective to serve as a guide for the preparation of similar 
apparatus on shijiboard. The substance of the following is taken from his report 
on the thermometers of the United States Commission of Fish and Fisheries, 1885. 
He used two Fahrenheit standards, made by J. Hicks, London, and veritied at the 
Kew Observatory. They were pointed to lifths of a degree, and a good reading could 
be made to tenths of a degree; they ranged from 10° to 120° F. 
A small comi»aring Jar Avas tirst used, iu which the instruments to be cmrected 
were immersed with the standard. A ring stirrer was ])rovided, and the jar had a 
wooden cover perforated with suitable holes to allow 
the instruments to pass through aud hold them in 
place. By agitating the stirrer up aud down, the water 
contained in the vessel was thoroughly mixed and a 
uniform temperature obtained. This simple contriv- 
ance answered very well for ordinary thermometers with 
bulbs exposed directly to the water, but admitted oidy 
two or three instruments at a time, owing to the com- 
OuT 48. — Small comparing jar. 
paratively small volume of water Avhich it contained. 
A larger jar with a capacity of 22 gallons was subse- 
quently used. 
For the “ zero point,” or 32° F., the thermometers 
to be tested were immersed in ffnely-broken ice con- 
tained in a large glass percolator, 12 inches wid ' by 
12 inches deep, with a small opening at the bottom for 
the escape of water as fast as the ice melted. Tins 
percolator is supported upon a suitable iron tripod and 
holds 8 thermometers without crowding. 
For deej)-sea thermometers, which are protected 
against water pressure by double glass bulbs and which are therefore slow and recpiire 
exposure to ai constant temperature for at least 10 minutes, Prof. T. Tiussel’s comparing 
jar was used, a sectional elevation of which is shown iu cut 10. 
The outer can A is of galvanized iron, 13^ inches high by 11 inches in diameter; 
B is an earthenware jar, 11 inches high by 8 inches in diameter; C is a tinned copi>er 
pot, fitting i>retty closely into B and suspended by a flange at the top. Inside of C 
is a (iopper frame, movable about a central spindle, to which the thermometers are 
attached. A ring stirrer moves in the space between A and B, and another between 
0 and the thermometer frame. When the temperatures to be observed are below that 
of the air, the spaces between A and B and within C are filled with water, that in the 
outer space being from 5° to 10° colder than that in contact with the thermometers. 
It is advised that they should be immersed for a time in water near the temperature 
sought before transferring them to the comparing jar. 
By agitating both bodies of water briskly with the stirrers and observing the 
standard thermometer in the inner jar from time to time, a sensibly constant tempera- 
ture will at length be reached, at which the gain in temperature of the water in the 
