CO BEXJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



The ruler or index, E, is made of brass, as long as the 

 diagonal of the table, and about two inches broad ; it has a 

 sloping edge, like that of a Gunter's scale, which is called 

 the fiducial edge. A perpendicular sight vane, F F, is fixed 

 to each extremity of the index, and the eye looking through 

 one of them, the vertical thread in the other is made to 

 bisect any required distant object. Upon the flat surface 

 of the index, there are frequently engraved scales of various 

 kinds, such as lines of equal parts, with diagonal scales, a 

 line of chords, &c. 



To the under side of the table, a centre is attached with 

 a ball and socket, or parallel plate-screws like those of the 

 theodolite, by which it can be placed upon a staff-head ; 

 and the table may be set horizontal, by means of a circular 

 spirit-level placed upon it for that purpose. 



Price, $20.00 to $35.00. 



Fig. 91. 



Surveyor's Cross. The surveyor's cross 

 (Fig. 91) consists of two pair of sights, 

 placed at right angles to each other. These 

 sights are sometimes pierced out in the 

 circumference of a thick tube of brass, or 

 sides of a square box, about three inches 

 in diameter. It has a socket, which, when 

 in use, is screwed on a staff, having a sharp 

 point at the bottom to stick in the ground. 

 The more improved instruments are made 

 octangular, having the intermediate angle 

 of 45 degrees also pierced. 



Price $3.00 to $6.00. 



Circumferentor, or Surveyor s Compass. (Fig. 92, next 

 page.) This instrument consists of a brass plate, usually 

 about fourteen or fifteen inches long, with sights at each 

 end, and in the middle thereof a circular box with a glass 

 cover, usually from five to seven inches diameter ; within 

 the box is a brass graduated circle, the upper surface divid- 

 ed into 360 degrees, and frequently subdivided into half 

 degrees, and numbered from the north and south points 

 each way from to 90. On the face of the plate are en- 

 graved the principal points of the compass, a fleur de lis 

 answering for the north. In the middle of the box is placed 

 a steel pin finely pointed, called the centre pin, on which is 



