MEASUREMENTS.

Distance.—­To measure the Length of a Journey by Time.—­The pace of a caravan across average country is 2 1/2 statute, or 2 geographical, miles per hour, as measured with compasses from point to point, and not following the sinuosities of each day’s course; but in making this estimate, every minute lost in stoppages by the way is supposed to be subtracted from the whole time spent on the road.  A careful traveller will be surprised at the accuracy of the geographical results, obtainable by noting the time he has employed in actual travel.  Experience shows that 10 English miles per day, measured along the road—­or, what is much the same thing, 7 geographical miles, measured with a pair of compasses from point to point—­is, taking one day with another, and including all stoppages of every kind, whatever be their cause,—­very fast travelling for a caravan.  In estimating the probable duration of a journey in an unknown country, or in arranging an outfit for an exploring expedition, not more than half that speed should be reckoned upon.  Indeed, it would be creditable to an explorer to have conducted the same caravan for a distance of 1000 geographical miles, across a rude country, in six months.  These data have, of course, no reference to a journey which may be accomplished by a single great effort, nor to one where the watering-places and pasturages are well known; but apply to an exploration of considerable length, in which a traveller must feel his way, and where he must use great caution not to exhaust his cattle, lest some unexpected call for exertion should arise, which they might prove unequal to meet.  Persons who have never travelled—­and very many of those who have, from neglecting to analyse their own performances—­entertain very erroneous views on these matters.

Rate of Movement to measure.—­a.  When the length of pace etc., is known before beginning, to observe.—­A man or a horse walking at the rate of one mile per hour, takes 10 paces in some ascertainable number of seconds, dependent upon the length of his step.  If the length of his step be 30 inches, he will occupy 17 seconds in making 10 paces.  Conversely, if the same person counts his paces for 17 seconds, and finds that he has taken 10 in that time, he will know that he is walking at the rate of exactly 1 mile per hour.  If he had taken 40 paces in the same period, he would know that his rate had been 4 miles per hour; if 35 paces, that it had been 3.5, or 3 1/2 miles per hour.  Thus it will be easily intelligible, that if a man knows the number of seconds appropriate to the length of his pace, he can learn the rate at which he is walking, by counting his paces during that number of seconds and by dividing the number of his paces so obtained, by 10.  In short the number of his paces during the period in question, gives his rate per hour, in miles and decimals of a mile, to one place of decimals.