90 



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



circular hole for viewing the bubble ; when placed against 

 a wall, post, or the like, will indicate if it is plumb, or not. 

 This is a valuable instrument for masons, carpenters, mill- 

 wrights, &c., for setting their work perpendicular, with more 

 expedition than the plumb-bob and string. 



Price, $2.00. 



Common Surveying Level. The annexed cut (Fig. 104) 

 is a representation of a spirit level of a plainer construction 

 than those that we shall describe, and though not having 

 the accuracy of the Y levels that are used by engineers, yet 

 will answer an ordinary purpose in the construction of 

 ditches, mill-seats, &c. The telescope is from twelve to 

 fourteen inches long, having adjusting tubes, and cross 

 hairs within, and is attached to a strong brass bar by screws 

 that have adjusting nuts ; the level is attached to the tele- 

 scope with the usual adjustments, and beneath the bar a 

 socket with a milled-head screw, for the purpose of firmly 

 mounting on the staff. Price, $12.00. 



Fig. 104. 



The T Spirit Level. (Fig. 105,) on the following page, 

 represents this instrument; it has an achromatic telescope 

 mounted in Y's like those of the theodolite, and is furnished 

 with a similar system of cross wires for determining the axis 

 of the tube, or line of collimation. By turning the milled - 

 headed screw, A, on the side of the telescope, the internal 

 tube, a, will be thrust outwards, which carrying the object- 

 glass, it is by this means adjusted to its focal distance, so 

 as to show a distant object distinctly. 



. The tube, c c, carrying the spirit-bubble, is fixed to the 

 under side of the telescope by a joint at one end, and a 



