288 
Journal of Agricultural Research 
Vol: XIV, No. 6 
The next arrangement which suggested itself as a means of measur¬ 
ing the fibers was the use of a micrometer caliper. A micrometer caliper 
graduated to read in hundredths of a millimeter and having a ratchet 
stop adjustment can readily be set so that contact upon the fibers is 
uniform and the fiber is not distorted when the contact is made. This 
micrometer is substituted in place of the lower jaw of the testing ma¬ 
chine (PI. 48, A) so that the diameters may be measured with the 
greatest speed and accuracy possible with a micrometer. A small hand 
lens (not shown in the illustration) was supported in front of the mi¬ 
crometer in order to make it possible to read the diameters of the wool 
fibers to a thousandth of a millimeter. 
The diameters of a number of fibers were measured at as many 
intervals as possible between the two jaws of the testing machine, 
after which the fibers were tested. The fibers broke in practically 
every instance at the place where the micrometer indicated the smallest 
diameter. A number of fibers were very carefully watched under a 
hand lens as they were being measured with the micrometer. It was 
observed that as the contact is being made the oval fibers twist so the 
measurement is made at the smallest diameter. Human hair and the 
hair from animals were tested with the same result. This led the 
writer to believe that he was justified in using the smallest diameters 
obtained by the use of a micrometer in computing the tensile strength 
(ratio of breaking strength to area of cross section) of the wool fibers. 
Another series of tests was made on the same samples as reported in 
Table I, but for five relative humidities, 40, 50, 60, 70, and 80 per cent, 
temperature 70° F. Every wool fiber tested was measured at three 
places between the jaws of the testing machine. The stretch of each 
fiber was recorded, together with its breaking strength, and the tensile 
strength calculated from the diameter of the fiber as found at the smallest 
point. The results of the measurement of the breaking strength are 
shown in Table II. 
Table II .—Breaking strengths of fibers at five humidities 
Breaking strength at a relative humidity of— 
Sample No. 
40 per cent. 
50 per cent. 
60 per cent. 
70 per cent. 
80 per cent. 
Aver¬ 
age of 
100. 
Aver¬ 
age of 
200. 
Aver¬ 
age of 
xoo. 
Aver¬ 
age of 
200. 
Aver¬ 
age of 
zoo. 
Aver¬ 
age of 
200. 
Aver¬ 
age of 
xoo. 
Aver¬ 
age of 
200. 
Aver¬ 
age of 
xoo. 
Aver¬ 
age of 
200. 
99 *. 
991. 
Dgm. 
66.8a 
67- 5* 
182.07 
194 - 70 
* 72 - 59 
« 7 - 77 
124* S 3 
Ia5*70 
Dgm. 
67.17 
Dgm. 
65-39 
66.44 
140.19 
*52-33 
196.67 
SIS- 74 
102-45 
108.42 
Dgm . 
69.92 
Dgm. 
67.50 
71.40 
* 45 *I* 
126.4a 
248 -88 
209-13 
X02.06 
108. 53 
Dgm. 
69 -45 
Dgm. 
54*67 
57-02 
* 59-43 
164.80 
2x0. 79 
190.64 
104.xo 
108.35 
Dgm. 
55*85 
Dgm. 
55-36 
52*34 
120.89 
*38.96 
X92. 71 
* 58 . 79 
103.30 
97**0 
Dgm. 
53*85 
P 94 . 
994... 
187.49 
146.26 
* 35 ‘ 77 
X62.12 
129*93 
. 
996.. 
* 95 *18 
206.21 
229.00 
200* 72 
* 75 * 75 
997 . 
997. 
135 *xa 
105.44 
105-39 
I06. 25 
xoo. 20 
