Most archers are aware of the fact that the size of a bow string has an appreciable effect on the cast of a bow. However, there is a considerable difference of opinion as to the magnitude of this effect.
The difference of opinion is probably due to the variations in the weight, size and shape of the bow used.
Wishing to investigate this problem in a rather extensive manner. Dr. Hickman enlisted the interest of Mr. Frederic A. Kibbe at Coldwater, Mich. He furnished the strings for the tests. He made up strings having 12, 14, 16, 18, 20, 22, 24, 26, 28 and 30 strands of Barbours Linen.
The 12 strand string weighed 108 grains and the 30 strand string weighed 254 grains. Each strand weighed approximately 12 grains.
The tests were made with a five-foot, eight-inch yew, a six-foot lemonwood and a five-foot, ten-inch maple.
Four different weight arrows were used. 280 grains, 370 grains, 537 grains, and 680 grains. These arrows were 26 inches long and were used at full draw.
The bow was clamped in a shooting device which was designed for testing arrows. Mounted on the shooting device is a member carrying a number of electrical contacts which are closed by a small pin attached to the arrow near the nock.
The electrical contacts are connected to a special spark chronograph which records the time for the arrow to travel from one contact to the next. In this manner the velocity and acceleration of the arrow may be obtained.
In these tests only the velocity of the arrow at the moment it left the bow was required. Therefore only the last three contacts were used. These contacts are six inches apart and are not engaged by the pin on the arrow until after it has left the string. The chronograph record gave the time required for the arrow to travel over two spaces of six inches each and also the total time required for the arrow to travel 12 inches. The extra contact was used only as a check.
The chronograph records intervals of time as small as .00005 seconds. The time required for the arrow to travel one foot in these tests varied from .0057 to .0093 seconds. The measurements are therefore in all cases accurate to better than one per cent.
Each of the three bows were tested with all four arrows and with all the strings. Great care was taken to insure that the bows were braced with the string at the same distance from the bow.
The weights of the bows at full draw were as follows: Yew, 47 pounds, Lemonwood, 43 pounds, Maple, 39 pounds.