PACING AS A MEANS OF MEASUREMENT. 183 



lines were paced at regular intervals. The accuracy of the pacer was 

 checked at each section line, and woodsmen selected for the work became 

 very expert, keeping count of regular steps through underbrush, through 

 windfalls, and even in deep snow on snow-shoes. It was found expedient 

 to adopt an arbitrary pace, 2,000 to the mile, and outcrops were located as 

 so many west and so many north from the southeastern corner of any par- 

 ticular section. Where the notes of different observers Avere to be studied 

 by one geologist a uniform pace was desirable, and it is probable that the 

 short pace, 2,000 to the mile, is a more regular unit of measure than a longer 

 stride ; for, being shorter than a man's average step, it would be less affected 

 by the varying conditions of the ground ; certainly no one who attemps to 

 stride beyond his ordinary step can pace regularly for any long distance. 

 Yet few men care to train themselves to a definite short step, and it is not 

 necessary where the distances paced are at once recorded in a plat of known 

 scale, since the unit of measurement then becomes a matter of indifference. 

 It is onl)/necessary that the pacer should know and record his average step,^ 

 and this can be ascertained by counting paces for half a day in walking a 

 known distance or by platting a day's route to an assumed scale and correct- 

 ing it by a map of known scale. 



The principal difficulty in pacing is to keep a correct count of steps, and 

 to avoid this we have found it desirable to count every fourth step only, 

 while yet giving to each footfall a digit or number. The mind readily rec- 

 ognizes a certain rhythm or time-beat on the fourth step, and it will un- 

 consciously repeat the total number of paces in time with successive steps, 

 adding one for each completed pace of four steps. Thus, starting out the 

 left foot first, the rhythm runs : Left, right, left, one, or 0, 0, 0, 1, 0, 0, 0, 2, 

 etc. ; and further on, left, right, thirty, five, or 0, 0, 3, 5 ; still further, left, 

 four, fifty, two, or 0, 4, 5, 2 ; when more than a thousand paces are num- 

 bered, one, three, seventy, eight, or 1, 3, 7, 8; the next pace, 1, 3, 7, 9 ; then, 

 1, 3, 8, ; and 1, 3, 8, 1, etc. Thus each step repeats the appropriate figure 

 and the four together give the total number of paces; the units change with 

 every fourth step, the tens only with every fortieth step, and the hundreds 

 and thousands each in their degree with less frequency. The repetition, un- 

 conscious though it comes to be, fixes the total number beyond the possibility 

 of loss.* 



The means of measurement being adopted, the method of recording is the 

 next step ; of these there are two : the plat on the traverse plane-table, and 



the plat in the note-book. ^ 



— — » 



* These methods of measurement suffice for the geologist on wheels or on foot, but they fail him 

 on horse-back. In discussing this paper Dr. G. M. Dawson described a method of "time survey," 

 which consists in riding a horse at a steady walk and noting the exact time consumed in riding 

 over each course. The time unit of the plat is a function of the gait of the horse and is influenced 

 by variations of the latter, and errors may creep in through disregard of momentary halts ; every 

 check .should be noted. But when carefully watched the time survey is accurate to about one- 

 fortieth of the distance. Dr. Dawson also referred to experience with a boat log in lake surveys. 



