OP THE UNITED STATES. 309 



sun to the observer. These remarks must certainly have 

 been often nmde ; and yet I have not seen that advantage 

 has ever been taken of them for the purpose here in view. 



A staff" is always a bad signal, as it will always be seen 

 differently according to the state of the illumination; and if 

 it is furnished with a flag for the purpose of discovering and 

 discerning it from other similar objects, tliis will easily mis- 

 lead the observer as to its aciual position, and certainly make 

 it appear to stand out of the peipendicular, if at any conside- 

 rable distance. Truncated pyramids are inconveniently 

 large, and require peculiar reductions according to the side 

 of them which is observable, and whicli may even change in 

 the course of the short time of observation, by the change 

 of the illumination. 



For the vertical angles tlie staff* cannot serve at all. The 

 point at wliich it is fastened into the earth can never be as- 

 certained with certainty, as it may be hidden by uneven 

 ground I)efore, or the ground from behind upon which it is 

 projected may be mistaken for it. Truncated pyramids may 

 be seen of different heights in different states of tl)e atmos- 

 phere. 



A signal showing itself detached from the ground on which 

 it stands, will also he distinguished far better than a much 

 larger one connected with the ground. 



All these remarks I might support with daily experience, 

 of which it will suffice to mention, that in a warm summer 

 day, the gilt hall of a steeple may be seen at a great distance,* 

 when the steeple itself is only su[)posed, and not actually dis- 

 tinguished. 



Making in 1798 a triangulation in Switzerland with a re- 

 peating circle witli two telcsc()i)cs, where the angles are 

 measured in the plane of the objects, and the determination 

 of the elevation of the triangle points being an ol)ject of in- 

 terest, 1 was desirous of a distinct signal which should l)e seen 

 equally in all directions: this lead me to the idea of forming 

 spheres elevated on poles. They were formed of barrel 



VOL. n. — s S 



