
Figure 28.—Mopex 621 SMALL PRIcE current meter. 
Only one contact chamber of the penta type was 
furnished with these meters when orders specified 
the 621 model. (Smithsonian photo 44537-E.) 
click to occur annoyed the men who used them on 
field work, the meters soon were provided with two 
interchangeable contact chambers, the extra one 
providing an electrical contact at each revolution. 
At first, these extra contact chambers were con- 
structed like those on the early 618 models, with two 
binding posts, one for the insulated wire and the other 
for the ground (see figures 24 and 29). On later 
models, however, the single-point chamber was made 
to correspond with the penta chamber in its outward 
appearance. In Gurley’s catalog, the number 624 
was assigned to meters that had been furnished with 
the two contact chambers. 
All model 624 meters used by the Survey were 
rated twice—a low-velocity rating for use with the 
contact chamber that produced one electrical contact 
per revolution and a high-velocity rating for use with 
For field purposes, both 
ratings usually were combined in a single rating table. 
the penta-contact chamber. 
To introduce the 621 model, J. C. Hoyt prepared 
an article for the Engineering News entitled “Recent 
Changes of Methods and Equipment in the Water 
Resources Work of the U.S. Geological Survey,” 
which was published on July 2, 1908. In that 
article Hoyt wrote that it was: 
. a meter that can be readily carried in the field and 
manipulated by one man under all conditions of velocity, 
depth, and width of a stream and with the various facilities 
for making measurements, which can be either a bridge, 
a boat, a cable and car, or by wading. 
A further description of the meter was contained 
in a paper entitled ““The Use and Care of the Current 
Meter as Practiced by the U.S. Geological Survey” 
that Hoyt presented before the American Society 
of Civil Engineers on September 15, 1909.!?  Tllustra- 
12 See the Transactions, vol. 66. 
Figure 29.—Mopev 624 SMALL Price current meter 
showing the earliest type of single-point contact 
chambers. On later models both the single- and 
penta-contact chambers had the same outward 
appearance as is seen in figures 28 and 30. (Smith- 
sonian photo 44537-C.) 
tions accompanying that article—considered a classic 
on the subject—show that an additional, although 
soon discarded, feature was being explored in con- 
nection with the 621 models. It consisted of an 
acoustic head which could be used interchangeably 
with the other two contact chambers, thus enabling 
the same instrument to be operated either as an 
acoustic meter producing a click at every tenth revolu- 
tion of the impeller, a penta electric Small Price 
current meter producing a click at every fifth revolu- 
tion, or a single-point meter producing a click for each 
Of these three facilities, only the second 
and third continued in use for some time. 
revolution. 
The next variation in the design of Small Price 
meters resulted from a suggestion offered by Clermont 
Calvert Covert, the Geological Survey’s district 
engineer in New York State. A boss was added to 
the upper limb of the yoke of the meter and was 
tapped to accommodate the lower section of a wading 
rod. Through its use, the meter could be suspended 
from a rod without resorting to the sliding hanger 
previously mentioned. This yoke became known 
as the Covert yoke. Meters on which it was fur- 
nished were identified by no. 623 in Gurley’s 46th 
(May 1912) manual and in subsequent manuals. All 
623 meters, like the 624 models, were furnished with 
both single- and penta-contact chambers. Represent- 
ative models of the 621 and 624 meters are shown 
in figures 28 and 29; a 623 meter, with a Covert 
yoke, is shown in figure 30. 
Because of a desire to have each improvement made 
applicable to previous models, most of the important 
dimensions on the Small Price meters have remained 
the same since the first model 617 was designed. 
All of the impellers, called bucket wheels, beginning, 
for example, with those placed on the earliest Acoustic 
62 BULLETIN 252: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 
