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The observations were made at a very quiet place on the River St. 
John, in New Brunswick, Canada, the whistles being sounded on one 
side by an assistant and the sounds listened to on the opposite side. 
Only times when there was no appreciable wind were chosen for observa- 
tion. When a wind sprang up in the course of a set of observations the 
work was discontinued and the observations discarded. In order to 
eliminate the effect of reflection from the banks, several different stations 
for sounding and directions for observing were tried in different sets of 
observations. The orifices of the whistles were always kept turned directly 
toward the observer. To avoid errors due to the tiring of the ear, in 
some cases the observations on the pairs of whistles were made 
first, and in other cases those on the eight whistles. Various devices 
were tried to eliminate the effect of bias in determining the distance of 
inaudibility. As regards the difficulty of determining the point at which 
the sounds became inaudible, this was found much less than was ex- 
pected. Nevertheless, there was always a space in which it was doubtful 
whether the sound was heard or imagined. The middle point of such 
a space was taken as the most probable position of extinction. 
As regards the success attained in attempting to make the different 
pairs of whistles of equal intensity, the following figures may be quoted. 
(These were the only cases in which the position for each pair of whistles 
was finally calculated. In general the position for each pair was marked 
by a stake and the mean finally taken for measurement.) In the first the 
mean distance was 1,693 feet and the distance of the separate observa- 
tionstions for the mean —28, —18, +5, +41, a total range of 69 feet. In the 
other the mean distance was 2,078 feet, and the distances from the mean 
were —39, —15, +9, +45, a total range of 84 feet. Here something must be 
allowed for unavoidable bias, but yet the result seems fairly satisfactory. 
The whistles were made of the stopped-organ-pipe form. In the ab- 
sence of facilities for the purpose their exact pitch was not determined 
until after the experiments had been made. The pitch was then de- 
termined by using a high pressure sensitive flame to find the nodes of the 
stationary waves produced by reflection from a wall. The semi-wave 
