Figure 30.—Mopet 623 SMALL Price 
current meter showing the Covert 
yoke. Except for the yoke, the 623 
and 624 models are identical. Each 
was provided with both single and 
penta interchangeable contact cham- 
bers. (USNM cat. no. 323836; 
Smithsonian photo 44537—D.) 
current meters, are interchangeable with the modern 
models. Except for a short time when the tailpiece was 
screwed into the early 617 yokes, any tailpiece will 
fit any yoke. Covert yokes can be substituted for 
any 621 or 624 yokes. So, whenever it became 
necessary to replace a part on a meter, it usually was 
replaced by its most modern counterpart. As a 
consequence, meters which had begun their existence 
as 617 models frequently became either partly or 
completely converted to 623 or 624 models. This 
practice has continued, enabling the U.S. Geological 
Survey to keep its thousands of meters up to modern 
standards and in good repair at minimum cost. 
With the introduction of the Covert yoke, both the 
Geological Survey, as represented by J. C. Hoyt, 
and the firm of W. & L. E. Gurley seemed satisfied 
with the meter’s design, and no further changes were 
made for several years. 
W. G. Price’s Final Design 
In the summer of 1920, W. G. Price, then in Yakima, 
Washington, examined the changes that had been 
made in his current meters and was displeased. 
The change that most irritated him was that which 
had been made in the upper bearing of the Small 
Price meter. In every talk or article he had pre- 
sented on the subject, he had emphasized the im- 
portance of both bearings operating in air pockets 
which would exclude water, silt, and grit. Despite 
his admonitions, the design adopted for the upper 
bearings on all the Small Price meters thus far manu- 
factured was identical to that which he had con- 
demned on the Ellis meters as far back as 1882. 
His first step toward combating that condition was 
to apply on August 19, 1920, for a new patent which 
had for its objective “the effective protection of the bear- 
ings from contact with water, dirt, or other foreign 
substances.” Patent 1,413,355 was granted him on 
April 18, 1922. During the almost two years while 

he was waiting for the application to be processed, 
another idea occurred to him. This was to use the 
same contact chamber to house both the single- and 
penta-contact facilities. That contact chamber was 
to be provided with two binding posts, one pointing 
forward, the other pointing rearward. The one point- 
ing forward was for use in measuring low velocities 
(the single-point contact); the one pointing toward 
the rear was for use when high velocities were to be 
measured (the penta contact). Price filed an applica- 
tion for a patent covering those features on November 
21, 1922, but patent 1,571,433 was not granted to him 
until February 2, 1926. A reproduction of the patent 
drawing is shown in figure 31. 
While Price was waiting for his patent to be 
awarded, W.& L. E. Gurley and the Geological 
Survey were collaborating on the development of still 
another new model, probably without any knowledge 
of the renewed interest Price had taken io the subject. 
On this occasion it was Carl H. Au, the Survey’s in- 
strument specialist, who provided the major ideas for 
their new design. 
‘‘Improved’’ Small Price Current Meters 
Carl Au (1876-1958), after having taught mechani- 
cal-engineering subjects for eight years at Worcester 
Polytechnic Institute, established an instrument shop 
in Washington, D.C. On one occasion his services 
were employed by the Geological Survey in connec- 
tion with the design and construction of the Survey’s 
stage-discharge integrator, an instrument used to 
convert graphical records of the stages in rivers into 
figures representing their average daily discharges. 
Officials were so impressed with his work on that 
instrument that in 1916 they invited him to become a 
senior engineer in charge of the Survey’s stream- 
gaging equipment—an invitation which he promptly 
accepted. During the earlier period of Au’s employ- 
ment, he devoted most. of his time and energy to 
PAPER 70: WILLIAM GUNN PRICE AND THE PRICE CURRENT METERS 63 
