Note I-3 — Chapter I · ITINERARY: ST. LOUIS TO ST. PAUL, AUGUST 9TH-SEPTEMBER 21ST, 1805.

In undertaking to follow a traveler, the first thing to ascertain is his "personal equation"—i. e., the probable error of his mileages. Pike traveled entirely by his watch, and all his distances are guesses based upon rate of progress—so many hours, so many miles. The way to approximate accuracy in this matter is to take him between two fixed points whose actual distance apart is ascertained, see what he makes of this, and adjust him accordingly. From St. Louis to Keokuk, by the present usual steamboat channel of the Miss. r., is 202¼ m.; say to the foot of Des Moines rapids, roundly 200 m. Pike's figures, as nearly as these can be got at, make this distance about 250 m. Hence we must discount his mileages 20 per cent., or one-fifth, as a rule. Taking one thing with another—changes in the channel in the course of the century, good or bad water, Pike's own feelings, errors of manuscript or print, etc., we shall find this deduction to work well; with the aid of such topographical data as we have, it will enable us to set most of his camps pretty closely. On the 10th, Pike gets left to bivouac on the bank at a point in Jersey Co., Ill., opposite Portage des Sioux, Mo., his barge being storm-bound somewhere above Alton, Ill., perhaps in the vicinity of Clifton or Randolph. The distance between Alton, first notable point above the Mo. r., and Grafton, last notable point below the Illinois r., is 16 m. Besides Alton and Clifton, places passed on the N. side are Shields' branch, Hop Hollow, Falling Rock cr., and Piasa cr.—some of the present isls. above Mobile isl. are Maple, Ellis, Search's, Piasa, and Eagle's Nest—the latter off Portage des Sioux.