534 Wisconsin Academy of Sciences, Arts, and Letters. 
water; the temperature of the mud could therefore be ascertained 
with sufficient accuracy. 
By this method, however, it is not possible to determine 
the depth below the surface of the mud from which is derived any 
Fig. 1 . The mud thermometer on the ice. This is the first one made, 
which was 3.5 m. long, with a hammer in one piece. The insulated 
wires and rope are seen attached to the top. The hammer with its two 
lines can also be seen. The thermometer is driven into the mud as far as 
the point where the hammer rests. 
given portion of the column of mud in the pipe, since the column 
is always shorter than the depth to which the pipe is driven. The 
upper strata of the mud are compressed, and as the pipe is driven 
down the mud is partly displaced and partly forced up into it. 
The deeper the pipe is driven the greater is the proportion of 
