524 FIRST REPORT UPON MAGNETIC WORK

The time arguments are given to the nearest half-minute; the
occurrence of a period after the minutes of any of them indicates that
its value is 0.5m. greater than printed, the table being so arranged to
economize space.

The table will be used as follows: Find the HOURS of the time
argument in the column marked "Hours"; then, between the heavy
lines which inclose the hours, find the MINUTES in the column marked
at the top with the current year. On the same horizontal line with
the MINUTES the azimuth will be found under the given latitude,
which is marked at the top. Thus, for 1897, time argument, Oh. 41m.,
latitude 38°, is the azimuth 0° 17'. For 1899, time argument 7h.
53m., latitude 36°, the azimuth is 1° 19'.

If the exact time argument is not found in the table the azimuth
should be proportioned to the difference between the given and tabular
values of said argument. Thus, if the time argument in the first of
the above examples (for 1897) was Oh. 39m., instead of Oh. 41m.,
the azimuth would be the mean between 0° 15' and 0° 17' or 0° 16'.
In a similar manner, if the latitude is nearer an odd than an even
degree, the mean of the azimuths for the next greater and next less
latitude will be used; thus in the above example for 1899, if the
given latitude was 37°, the mean between 1° 19' and 1° 21', or 1° 20',
would be corresponding azimuth. The table has been arranged to
give the azimuths, as exemplified above, by simple inspection. No
written arithmetical work is required, all being performed mentally.
It will generally be sufficient to take the nearest whole degree of lati-
tude and use it as above directed; for a few values near the bottom
of the table, for example, the latitude may be taken to the nearest
half degree.

The attention of the surveyor is directed to the fact that he should
always use one day of twenty-four hours as the unit when he subtracts
the time of culmination from the time of observation. In any case
when the time of upper culmination taken from Table XV, for
the given date, would be numerically greater than the astronomical
time of observation, the former time will be taken out for a date one
day earlier than the date of observation. The surveyor will decide