HELIOTROPES. 



53 



as the simplest backwoodsman can manage it; and the triangulator can 

 firmly fix all range stakes upon one visit to the station, and be sure of seeing 

 the flash as he observes from each of the surrounding stations in turn. 



Two other forms are in use, the Coast Survey type and the Steinheil. 

 See Figs. 5 and 6. The former consists of a telescope which is provided 

 with a screw for fastening it into any con- 

 venient support or upon the theodolite. Upon 

 the telescope is a mirror and two rings, the axis 

 of the rings as well as the center of support of 

 the mirror being parallel to the line of sight 

 of the telescope. The telescope being directed 

 upon the observing station, the mirror is so 

 turned as to reflect the sunlight through the 

 rings and necessarily to the observing station. 

 In many cases the use of a second mirror is 

 necessary, owing to the relative position of the 

 two stations and the sun, and such a mirror 

 forms a part of the outfit. This form is little 

 used, on account of its liability to get out of 

 adjustment. The Steinheil heliotrope is ac om- 

 pact little instrument, which can be carried in a 

 case like a pair of field glasses. It consists of 

 a small sextant mirror, the two surfaces of which 

 are as nearly absolutely parallel as possible. 

 This mirror lias a small hole in the center of 

 the reflecting surface. Below this central hole 

 is a small lens in the shaft carrying the mirror, and below the lens is 

 some white reflecting material, as plaster of Paris. The mirror is so mounted 

 that it has four different motions, two about its horizontal axis and two 

 about its vertical axis, each of which can be separately bound or controlled 

 by clamps or friction movements. To use the Steinheil, it is screwed into 

 some wooden upright, as the side of a tree, in such a position that the main 

 axis carrying the lens and plaster of Paris reflector shall be parallel to the 

 sun's rays. The observer standing behind the mirror receives from the rear 



Fia. 6.— Steinheil Heliotrope 



