ia 
PSEA AP ON NE a by es ST 
C. Abbe on the Repsold Portable Circle. 313 
ingly well the rough usage to which they must needs be sub- 
jected _in journeys of thousands of miles. A heavy tripod is 
rovided, and the means for leaving a suitable simple mark at 
any station, The vertical circle, without being in the least taken 
to pieces, is received as a whole into its small neat case in which 
two clamps firmly fasten it, an outer thick leather cover with 
stakes of wood support the feet of the tripod and remain to 
spor me the horses having been unhitched 
compared with the one to be used in the observations. The e 
amination of the state of the instrument and the adjustment of 
the verticality of the vertical axis follow, and in a few minutes 
after observing the Sun or Moon, Po laris is in the field of view, 
Although one iiearinisiala uly of time is necessary, it is bet- 
ter to make two, arranging tie) — as follows : 
1. Com ee of chrono 
. Observation of pair of stars for time. 
. Reading of barometer and thermometer. 
Comparison of chronometer. 
The observations are now complete and the party may pro- 
ceed te the next station; if any considerable time elapses the 
departure should be immediately preceded by another compar- 
ison of chronometers. 
The time spent at a any station must depend upon the skill, en- 
ergy and self- nti of the “oa rver. In the expedition by 
Déllen and Hiibner in 1855-56 in the province of Perm, cases 
occur where pain station distant twenty-five to forty miles 
from each other, have been thus occupied within the space of 
thirty-six hours, the = spent at each being about three hours, 
the intervening distances being travelled over very ordinary 
Toads. It is often very ;siviabes to work expeditiously in order 
to improve a few days of consecutive clear weather and secure 
@ quick return to the starting Aen ites fiend ent 
the chronometers to a lon ng absence 
changes, This latter point is one sequin eps an) intelli 
CO ~T SH OUP OG bO 
° 
le 
3 
5 
& 
a. A 
° 
[=] 
2 
so 
~ 
= 
° 
Lac} 
= 
d 
oy 
“3 
e 
= ¥ 
> 
i] 
Qu 
oD 
