and weighs only 5 Ibs. It is especially adapted for use with a 15 x 15 

 planchette and the so-called Graton Traverse Alidade with sight 

 vanes, declinatoireand small circular bubble, for preliminary surveys 

 in remote districts. The 15 x 15 planchette is large enough for a 

 township plotted 2 in. per mile. 



* The planchette is secured to the head mechanism in much the 

 same manner as just described. If the knurled head is turned to 

 the left, the key-bolt is released; if turned to the right, the connec- 

 tion is tightened. The planchette may be revolved on the circular 

 seating and is held in position there by friction. There is no 

 means of leveling the table except by carefully choosing the position 

 for the spindle legs. 



The Planchette 



Fig. 27 



The planchette is a drafting board of suitable 

 size made of well seasoned flawless pine and con- 

 structed in sections to prevent warping. It is rarely 

 larger than 24 x 30 inches (6.1 x 7.6 dm). The 

 intermediate size is 18 x 24 (4.6 x 6.1 dm) and the 

 traverse size, 15 x 15 (3.8 x 3.8 dm). In the under 

 side is inserted some sort of mechanical provision 

 to fasten the same securely to the tripod, as indicated 

 in the upper portions of Figs. 25 and 26. 



For attaching the paper to the board various 

 methods are in use. When a survey extends at 

 great distance in one direction, the paper has been 

 fed continuously from rollers beneath the board. 

 That portion which is in use can be held in position 

 by tension from the rollers or by spring clips. 

 Thumb tacks are not recommended* because they 

 interfere with the unrestricted movement of the 

 alidade. 



What is generally conceded to be the best 

 practise is to countersink, in the outer edges of the 

 planchette, a system of six or eight threaded sockets 

 and fasten the paper with screw-tacks that are set 

 down flush with the surface, t These keep the 

 paper from lateral displacement and prevent it from 

 being ripped from the table in high winds. Our 

 planchettes are usually made in this way, but we are 

 prepared to supply the nickle plated spring clips 

 on request. The declinatoire, which may be 

 mortised into the edge of the planchette, is shown 

 in Fig. 27 and described on page 48. 



* Plane Surveyin. A. E. Phillips, c . 1910. p. 175. 



\ Topographic Surveying, It. .if. ICilson, 1900. p. 177. 



45 



