333 SURVEY OF THE COAST 



half an inch farther, another short slit, at right angles to the 

 former. By these the paper was slided and held upon the 

 arm of tlie magnifier, and screwed to it along with its tube. 

 Holding a light on the opposite side of the circle properly, 

 the light will be reflected very well on the divisions, and give 

 a very good reading. During the day the free light will [lave 

 the same effect. 



It is useful to know exactly the angular distances of the 

 wires in the telescope, and the values of the divisions of the 

 level. The first are very easily determined by pointing 

 upon a well defined object with the different wires and read- 

 ing the verniers. The last are equally easy to determine in 

 these instruments, having readings to the level motion, by 

 placing the level on all divisions successively, and reading 

 all four verniers. It is proper to repeat these observations 

 when made, as the determination has regard to a very small 

 quantity. Methods for this purpose will easily suggest them- 

 selves to a skilful observer, and a very good use may be 

 made of the results, when accidents have disturbed the usual 

 regularity of an observation. Still I do not approve of a 

 method suggested sometimes, viz. reading the level, though 

 not fully adjusted, and keeping account of its standing at each 

 observation. 



In one of these circles, the intervals of the wires were 

 8' 0.5 '',3 in the arc, and ten small divisions of the level sub- 



Methods of observing a Series of Vertical Jingles uith t/ie Re- 

 peating Circle. 



The instrument being well adjusted and levelled by means 

 of the large level of the circle, I place the front telescope 

 before the observation upon any convenient point of the cir- 



