"تقرير عسكري عن جنوب غرب بلاد فارس، يتضمن أقاليم خوزستان (عربستان)، لورستان، وجزءًا من فارس" [‎١‎١‎٤] (٤٦٦/١٥٧)

114
The most that a traveller in Persia, uaconnected officially with the Gov-
„ ■« a * eminent, can do towards surveying the country that
Kecord of route. t > i-xi ^ ,
he passes through is to keep a traverse ot the road,
and to take angles to a few of the most conspicuous points, noting all angles in
a pocket book, and the hoar at which they are taken. The average rates at
which a mule travels are fairly uniform over plains and over hills.
Such a traverse, checked by latitudes and longitudes, gives very fair results,
especially if the rate of the chronometer can be checked frequently.
In the present case the half chronometer watch was checked at Muham-
merah, Kdm, Isfahan, Bandar-Dilam, and Bushire. Its error thus determin
ed enabled a daily rate to be struck between Muhammerah and Kum, Kum
and Isfahan, Isfahan and Bandar Dilam. This gives approximate results only,
for it was found that the daily error varied with the temperature and length
of the stage made.
Chronometers and half-chronometer watches and aneroids are rated and
checked before issue under conditions of absolute rest, whereas when in use
the traveller subjects them to conditions of unrest and jerk. The error result
ing from such usage, which is inseparable from that of travel, can be best
determined by striking rates as often as possible and by working relatively
to each known point as met with in succession. The chronometer should be
a good one to begin with and a steady goer and be tested before issue for
one month under conditions similar to those under which they will he used,
i.e., by being carried about on foot and on horseback. The same remark applies
to the aneroid barometer, which should he likewise tested in a similar manner.
For the corrections allowed for in determining the heights of the points given
in this report, see page 28.
The variation of the compass is so small that it may be neglected in
rapid compass work.
The following were taken as the positions of the above-mentioned places
Latitude. Longitude.
Muhammerah ... 30° 26' (Y' ... 48° 13' 0 7
Kiim ... 34° 41' 30"' ... 50° 53' 54"
Isfahan ... 32° 35' 30 7 ... 51° 39' 0"
Bandar Dilam ... ... 30° 0' 0 7 ... 50° 10' 0 7
Bushire ... ... 28° 59' 7" ... 50° 49' 24"
The instruments used were, for the road traverse, pocket compass, watch
pattern, large size, %" inches diameter; an aneroid barometer, 4" inches diame
ter ; and for astronomical observations a silver half chronometer watch, a
6-inch Hadley's sextant and a George^s artificial horizon.
The use of the pocket compass attracts little attention, as it is held to
the breast and not to the eye, and the results that it gives are astonishingly
accurate.
So long as you explain that the sextant is a watch, by means of which yon
regulate, by observing the sun and stars, the one that you wear, great
interest will be taken in seeing the tamdshd, and the purity of your intentions
will not be doubted.
If possible, a swung ship^s chronometer should be taken.