3o Art of Travel.
books ought to open. Four pages go to a day ; of these the pages 1 and 2 are alone represented in this book, pages 3 and 4 being intended to be left blank.
The bold figures, 17 and 18, in the right-hand corners of the form I give, show how the pages should be numbered. The lines in p. 18 should be faint blue.
e. 3, Calculation Book.-This should be of the same size and shape as the Log Book, and should contain outline forms for calculations. The labour and confusion saved by using these, and the accuracy of work that they ensure, are truly remarkable. The instruments used, the observations made, and especially the tables employed, are so exceedingly diverse, that I fear it would be to little purpose if I were to give special examples : each traveller must suit himself. I will, therefore, simply make a few general remarks on this subject, in the following paragraph.
Number of Observations requiring record.-A traveller does excellently, who takes latitudes by meridian altitudes, once in the twenty-four hours ; a careful series of lunars once a fortnight, on on average ; compass variations as often ; and an occultation now and then. He will want, occasionally, a time observation by which to set his watch (I am supposing he uses no chronometer). He ought therefore to provide himself with outline forms for calculating these observations, even if he finds himself obliged to have them printed or lithographed on purpose ; and in preparing them, he should bear the following well-known maxims in mind :
Let all careful observations be in doubles. If they be for latitudes, observe a star N. and a star S.; the errors of your instruments will then affect the results in opposite directions, and the mean of the results will destroy the error. ' So, if for time, observe in doubles, viz., a star E. and a star W. Also, if for lunars, let your sets be in doubles-one set of distances to a star E. of moon, and one to a star W. of moon. Whenever you begin on lunars, give three hours at least to them, and bring away a reliable series; you will be thus possessed of a certainty to work upon, instead of the miserably unsatisfactory results obtained from a single set of lunars taken here and another set there, scattered all over the country, and
)F - www.fastio.com