by simply sliding the tube down \\aid to the stop-catch, as indicated 

 in the illustration. The planchette should be set about elbow 

 height, but continuous bending over it is a tiresome occupation. 

 Frequently the eyepiece prism is used so that the operator may 

 look directly downward when talcing sights. This new device makes 

 such an expedient the more desirable, particularly as one need not 

 remove his hat. When this eyepiece is used, a little heavier sun- 

 shade is employed. The extra ocular shown in Fig. 28 can be 

 substituted whenever desired. 



The Vertical Arc is of 60 duration with a single vernier 

 centered at the 30 mark. This ma-ies it impossible to confuse 

 small angles of elevation or depression; 30 must either be sub- 

 tracted from the observed result or <vice<versa. Occasionally there is 

 supplied, beside the vertical arc, the Beaman stadia arc as shown 

 above and in Fig. 65 > p. 115. 



The Pillar is aluminum, cord wound, either 3,}^ or4j inches 

 high, as preferred, and the Base Rule is a brass blade 16 X 2}{ or 

 1 > 3 in. , as desired. The contact surface of the base rule has been 

 previously covered with a light brown drafting paper which 

 could be cleaned with a pencil eraser, or fine emery paper, but we 

 have recently adopted a white enamel finish, which can be washed 

 and is very satisfactory. 



Level Vials are still preferred by some topographers mounted 

 in coordinate horizontal planes on the base rule, or countersunk in 

 the planchette, but their adjustment against even slight inequalities 

 of the base rule has been found to consume much unnecessary time. 

 We are prepared, however, to furnish this system in place of the 

 circular level if so specified. 



The Bulls Eye Level has no gauged sensibility but is amply 

 accurate for the intended purpose and does not distract the operator 

 with indicated errors of no concern. At any rate, as a measure of 

 economics, the leveling device should Demounted on the base rule 

 for it may be thus applied to any planchette. If one wishes to 

 secure unusual accuracy in leveling the planchette for any reason, 



47 



