A SECOND REPORT ON LIMNOLOGICAL APPARATUS 
Edward A. Birge 
Notes from the Biological (Laboratory of the Wisconsin Geological 
and Natural History Survey. XIX. 
This paper on limnological apparatus continues one published 
by Mr. Juday in these Transactions (18:566-592, 1916). It 
describes certain pieces of apparatus constructed and employed 
by this Survey, chiefly those employed in studying the lake tem¬ 
peratures. 
I. Mud Thermometer (Text figures 1, 2, 3) 
In March, 1908, several observations were made to determine 
the temperature of the mud at the bottom of Lake Mendota. The 
results showed temperatures which rose from 2.6° C. at the sur¬ 
face of the mud to 8.8° or 9.0° about 3 m. below the surface. For 
this purpose there was used an iron pipe about 3 m. (10 ft.) 
long and 10 cm. (4 in.) in internal diameter. The pipe was open 
at the bottom, covered by a cap at the top; the cap bore a ring 
to which was attached the rope for suspending the apparatus. 
This instrument was used while the lake was covered by ice. It 
was lowered to the bottom by a rope which was attached to a 
windlass; and it was driven into the mud by a weight which rested 
on the top of the pipe when it was lowered. The weight was 
raised by means of two small lines and then dropped, sliding down 
the rope and striking the top of the pipe; and the pipe with the 
contained mud was then drawn to the surface and laid on the ice. 
At regular intervals along its side there were small holes through 
which thermometers could be pushed into the mud so as to ascer¬ 
tain its temperature. The mud is a fine-grained, pasty material, 
through which water passes very slowly, practically not at all 
during the few minutes necessary to raise and take it from the 
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