LIMNOLOGICAL OBSERVATIONS IN THE UPPER MISSISSIPPI. 
353 
BOAT AND EQUIPMENT. 
The question of a boat for hydrobiological work is of great importance, as the 
success of the exploration very often depends upon its suitability. Many diffi- 
culties arise when one has to work with one boat and has to visit different places 
on the river, parts of which are shallow, with sloughs and bays, while other parts 
widen into large lakes. During my investigation an ordinary fishermen’s flat- 
bottom launch, 22 feet long, was used. All equipment and laboratory instruments, 
including a microscope, were placed in three specially constructed field chests 
and the chests were fixed on the stern, which in a short time could be transformed 
into a small field laboratory (fig. 2). An awning protected the instruments from 
showers. A pump with hose and a graduated tank were fixed on the bow. 
Fully loaded and with two men aboard the boat drew 25 inches of water. It 
was convenient to have all instruments at hand and to be prepared to start the 
observations at any time or place, yet difficulties arose and many serious troubles 
even were encountered when it was attempted to reach the shallow parts of the 
river. In July and August the river was so low that even our boat was too deep 
to reach many of the sloughs and lateral channels. This was a great handicap 
to the whole work, because the observations in sloughs and bays are sometimes 
of greater importance than those in the main channel of the river. It was 
especially difficult to make observations on the overflowed area of Lake Keokuk, 
where branches of trees and bushes rising above the surface of the water form 
impassable thickets. Attempts to collect the material on foot here were also 
unsuccessful, for the bottom was covered with a thin brown mud incapable of 
supporting the weight of a human body. A small rowboat would be more suitable 
in such places if the equipment were not too heavy. 
On windy days the water in Lake Keokuk and in Lake Pepin may become 
too rough for the safety of a flat-bottomed river launch. We had two accidents 
with our boat during storms on Lake Keokuk, and once the boat sank. Fortu- 
nately this happened near shore, but of course it caused considerable delay in the 
work. On Lake Pepin the weather was still less favorable, and the launch was 
changed for a keel boat (fig. 5). 
Instruments . — For measuring temperature two reversing Negretti and Zambra 
(Richter) thermometers Nos. 281 and 283 were used, both of them having previ- 
ously been tested by the United States Bureau of Standards (certificates No. Ttt- 
31154), and the data of observations have been corrected accordingly. The rate 
of current was measured with Price’s electric water current meter, No. 970, manu- 
factured by W. & L. E. Gurley (for description see Hoyt and Grover, 1916, pp. 9-12), 
this instrument also having been tested by the United States Bureau of Standards 
(test No. 31795). The current meter was not received until after the 15th of 
August, and during the first weeks of the investigations a simplified method of 
floats was used. A bottle filled with water until it nearly submerged was allowed 
to drift beside the boat; a distance of 20 feet had previously been measured on 
the gunwale of the boat and marked by two horizontally fixed sticks; time was 
taken first when the bottle passed under the forward stick and again when it passed 
