METHODS OF MEASUREMENT. 29 



was frequently a change in the speed of the treadmill. This change 

 was gradual and could not be easily detected. It often happened, 

 therefore, that when the speed was properly adjusted at the beginning 

 of the experiment it would be found that as time passed the rates of 

 walking for the different periods varied slightly from each other. 

 During the walking experiments in which high grades were employed, 

 use was made of the brake Q, Qi, bearing on a pulley fixed to the motor 

 shaft, to aid in securing satisfactory speed adjustments. (See fig. 1.) 

 Angle of ascent, By means of two nuts sunk in the head of the tread- 

 mill frame and two long screws (see N, and NI, fig. 1, p. 19), it is 

 possible to elevate the front end of the treadmill to an angle of slightly 

 over 45. A spirit-level (0 in fig. 1), fastened to the front of the tread- 

 mill, indicates when both sides have been adjusted equally, so that the 

 belt will run smoothly and true. To determine the elevation of the 

 treadmill, a light wooden triangular frame was constructed, which is 

 shown in figure 6. This was pivoted at A and E and could be ad jus ted 

 at B, by means of a slot and set-nut. The distance between A and C 

 was exactly 100 cm. When used to find the angle of elevation, this 

 frame was placed upon the walking surface of the treadmill, with the 

 edge AE resting on the leather belt. It was then adjusted at B until 



FIG. 6. Framework used in 

 determining the angle of 

 ascent. 



the surface A B was perfectly level, as shown by the spirit-level S. 

 The elevation DC was next measured and used to find the sine of the 

 angle, or the "slant-height." Since AC is 100 cm., the slant-height 

 may be readily expressed as per cent. Accordingly, when the grade 

 is given as 10 per cent, it is meant that the subject in walking a linear 

 distance of 100 meters raised himself to a height equivalent to 10 meters. 

 It should be borne in mind that for the 100 linear meters thus walked, 

 the energy expended over and above the standing requirements was 

 made up of the energy required (1) for the elevation of the body and 

 (2) for transporting the body over the horizontal component. This 

 horizontal component was found from the cosine of the angle. Thus, 

 the subject, in walking on a 10 per cent grade at a rate of 100 meters 

 per minute, walked a linear distance of 100 meters and the vertical 

 component would be 10 meters, while the horizontal component would 

 be 100 X cosine 5 44' 30", or 99.5 meters. 



