244 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
depth of 25 feet. In this pond research investigations of underwater . 
explosions and explosive tests against models of ship structures are 
carried out. 
Information can be obtained on the trajectories of model bombs and 
torpedoes after impact with the water surface by experiments made in 
the new transparent-wali tank, using high-speed motion pictures to 
record the paths of the models. The new tank has glass windows 
forming one side and one end; it is 25 feet long, 9 feet deep, and 414 
feet wide, filled with continuously filtered, crystal-clear water to insure 
clear photographs. The windows are three-quarters of an inch 
thick “tempered” glass, four times as strong as ordinary plate glass 
of the same thickness. Intense photographic illumination is necessary 
to obtain good film records of the objects moving through the water. 
The circulating-water channel, now nearing completion, is an 
unusual hydraulic testing facility, both as to type and size. Essen- 
tially it consists of an open-top test section 22 feet wide and 60 feet 
long in which a stream of water 9 feet deep flows at a maximum speed 
of 10 knots. The object under test will be held stationary in the moving 
stream and the forces exerted by the water measured by suitable dyna- 
mometers. The walls and bottom of this channel contain windows 
approximately 4 feet by 114 feet through which both visual and photo- 
graphic observations can be made. 
The chief advantages obtained by testing in the circulating-water 
channel are that the object undergoing test can be viewed and photo- 
graphed from all sides and that the tests may be carried on for an 
indefinite period without stopping as at the end of a straight towing 
run. 
The objects tested in this channel will consist of ship models, torpedo 
shapes, mines, and special devices which cannot be tested as well by 
towing in still water. The water channel will complement the existing 
turning basins and water tunnels but will not supplant them. 
In order that such a large stream of water may be circulated at con- 
stant speed with uniform flow throughout the test section, a structure 
about 150 feet long and 45 feet high is required. The water is pumped 
through the channel by two 1214-foot-diameter propeller-type pumps 
driven by direct-connected 1,250-horsepower electric motors. These 
motors rotate at constant speed and the rate of flow of the water is 
regulated by adjusting the pitch of the propeller blades while running. 
The wind-tunnel building is located to the west of the main building. 
It contains two steel wind tunnels, each with a closed rectangular test 
section 8 feet by 10 feet, and with single return passage. These tunnels 
are equipped with 4-bladed, 16-foot-diameter wooden propellers, one 
driven by a 1,000-horsepower motor, the other by a 700-horsepower 
motor. These motors are controlled by the Clymer system which per- 
