540 Wisconsin Academy of Sciences, Arts, and Letters. 
The thermometer was lowered to the proper depth—say 1 m.— 
and allowed to remain until it had acquired the temperature of the 
water. In order to ascertain this fact, the instrument was drawn 
to the surface and examined from time to time until the‘index 
ceased to fall When it was finally returned to its place, the slide 
was drawn from the bulb; the thermometer was exposed to the 
sun; after five minutes it was drawn to the surface, and the rise 
of the alcohol above the index was noted. The instrument was 
then lowered to another depth—say 2 m.—and the process was 
repeated. 
This instrument was successfully used by both Mr. Juday and 
myself on a considerable number of lakes; but it was very slow in 
its operation, requiring 15-20 minutes for a single reading. Many 
series of observations were lost because of clouds coming on dur¬ 
ing the long time required even for two readings. In all cases 
the lapse of time was so great as to give the sun ample opportunity 
for change. 
The second instrument was a great improvement on the first. 
Its centra] part is a sensitive black-bulb mercurial thermometer 
with a scale 25 cm. long extending from -2° to 32°, divided to 
0.2° C. and mounted in vacuo. It is fastened into a frame 65 cm. 
long and 10.5 cm. wide, made of 12-mm. brass tubing. On this 
frame is a sliding cover for the bulb, operated by cords which 
lead to the surface. The thermometer is read from the surface 
by a telescope inserted into a carrier which is attached to the 
top of a brass tube 5 cm. in diameter. This tube is composed of 
pieces of tubing, each about 85 cm. long; these can be screwed 
together with water-tight joints and are added as the depth of 
observation increases. The bottom joint of the tube is screwed 
into a base piece which has a glass center. This base is movable 
on the frame so that it can be fastened securely above that part 
of the thermometer scale which corresponds to the temperature of 
the water. 
Two persons are employed with this instrument, one to read 
and one to record. The temperature of the water at the point 
of observation is first ascertained by an ordinary deep-sea ther¬ 
mometer. Ice water is poured over the vacuum bulb, and the 
black-bulb thermometer is thus cooled down a degree or more be¬ 
low the temperature of the water. The instrument is then lowered 
into place, and after the outer bulb has acquired the temperature 
of the water the slide is drawn and the thermometer is exposed 
