96 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



of the rod, passing through pulleys in the ends, and is at- 

 tached to the lower part of the box. By means of this cord 

 the target may be moved up or down, when out of the 

 reach of the vane man. Price, $5.00 to $8.00 each. 



Portable Levelling Staves. Two mahogany station-staves 

 generally accompany the spirit-level ; they consist of two 

 parts, capable of being drawn out when considerable length 

 is required. They are divided into feet and hundredths, or 

 feet, inches, and tenths, and have a sliding-vane, with a wire 

 placed across a square hole in the centre, as shown in 

 Fig. 107 : this vane being raised or lowered by the as- 

 sistant, until the cross-wire corresponds with the horizontal 

 wire of the telescope, the height of the wire in the vane, 

 noted on the staff, is the height of the apparent level above 

 the ground at that place. 



When both the staves are used, they should be set up at 

 equal distances on each side of the spirit level : the difference 

 of the heights of their vanes will be the absolute difference 

 of level between the two stations. But when one staff only 

 is employed, the difference between the height of the vane 

 and the height of the centre of the telescope of the instru- 

 ment, will be the apparent difference of level, which, if the 

 distance between the staff and instrument is great, requires 

 to be corrected for the curvature of the earth. 



Price, $5.00 to $8.00 each. 



> 108< Angle Meter, or Level 



for Slopes. (Fig. 108.) 

 This level, used for mea- 

 suring the angle of strata 

 in mines, geological form- 

 ations, and any inclination 

 or slope, consists of a stout 

 brass plate, about 6 inches 

 long, jointed at one end 

 to another plate, having a 

 level at the side, and hav- 

 ing a graduated arc at- 

 tached to the lower plate, 

 and moving in a slide on the back of the level plate, and also 

 jointed for portability. In use the lower plate is placed on 

 the slope, and the jointed plate moved till the bubble of the 



