Lewis's Notes

Page 9 of 13

[Immediately following Patterson's document appear, in Lewis's handwriting, these Statistical Tables, undoubtedly those recommended by Patterson in his letter to Jefferson of June 18, 1803 (see Editor's Foreword). The columns extend across four double pages (13 in. x 7 in.). There are no entries but the headings in any of the columns.]

Statistical Table

Table 18

[Continuing in Lewis's hand, p. 30:]

Explanations and notes on the foregoing table

c. denotes - that the numbers to which it is prefixed is the result of calculations. –

ob. Denotes that the numbers to which it is prefixed are the result of observation only and remain to be calculated.

f. or s. in collumn 5th denotes that the watch is too fast or slow the number of minutes seconds &c to which it is prefixed. –

g. or l. denotes gain or loss of watch.

. LL. or U.L. Denote sun's center, his Lower Limb, or Upper Limb. –

B or F denote the back or Fore observation - it may be well here to remark that all the back observations are made with an octant & artificial horizon, and that the aparent altitudes as set down in collumns No. 8, 10 & 14 where the instrument error is designated B. are always to be understood to express the number of Degrees ' & "" &c. shewn by the graduated limb of the octant at the time of the observation, and is the complyment only of 180° or the double altitude of the object observed. Thus the sum given by the back observation as set down in the table are subtracted from 180° and the remainder is the double apparent altitude of the object observed, which divided by 2 and is the same.

Lewis's record of observations made
at the Musselshell River

Page 31 in the Astronomy Notebook

Page 31

[p. 31:]

the post meridian observation of the preceding [i.e., following] observation was made at the entrance of the Musselshell River. -------

Point of observation No. 21.

May 20th 1805

At the point of land formed by the junction of the Musselshell River and the Missouri. observed meridian altitude of 's L.L. with octant by the back observation ---------------------------- 59°50' -""
Latitude deduced from this observation 47. 00. 24.6


May 21st 1805 Point of observation No. 22.
On the Lard. shore at the commencement of the 5th course of this day observed time and distance of the 's and moon's nearest limbs, the East-- with Sextant


N ot only did Lewis never employ the Statistical Tables sketched out above, he never consistently used all of the abbreviations listed in the "Explanation and notes." Curiously, the material that follows on the very next page indicates that he carried the Astronomy Notebook throughout the expedition, for there he entered data relating to the Meridian Altitude he and Clark observed at the confluence of the Missouri and Musselshell Rivers on 20 May 1805.

The first data set is similar to the one in Clark's journal entry (Moulton, 4:174), except that Clark's second bearing reads S85°W there, whereas Lewis recorded S83°W, which would have been closer to correct. Lewis, unfortunately, arrived at 58 degrees for the sun's altitude, which obviously is wrong. Clark, either while he and Lewis were taking the observation or else from the notes of whoever was helping Lewis at the time, wrote down a double altitude of the sun's lower limb as 48°20'15"", which was about right. Maybe Lewis was using this page as a worksheet for a discussion with Clark, and simply crossed out the whole second line containing his erroneous conclusion, without seeing any need to revise it.

The Lunar Distance Lewis deduced from an unrecorded set of 12 observations on the 21st, at Point of Observation No. 22, is identical to the entry in his journal (Moulton, 4:177) as far as the figures are concerned.


Funded in part by a grant from the NPS Challenge-Cost Share Program.