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approved ; by the addition of a pair of small sights it is 

 sometimes used as a surveyor's compass. For this instru- 

 ment the author received, a few years since, from the 

 American Institute, a silver medal ; and another was 

 awarded the last year, by the New York State Agricul- 

 tural Society, at its annual fair held in the city of New 

 York. 



The horizontal plate is nine and a half inches diameter, 

 graduated into degrees and half degrees, numbered from 

 to 360. The vernier plate is eight inches diameter; at 

 one portion it is shampered off to an edge, containing a 

 vernier divided from the middle both ways into thirty 

 parts, numbered 0, 10, 20, 30, subdividing the graduations 

 on the lower plate to single minutes. These two plates 

 are connected together by a conical axis ground in each 

 other, having an even and steady motion when turned. 

 The compass-box is nearly seven inches diameter, within 

 which there is a graduated circle divided into 360 degrees, 

 and subdivided to half degrees, numbered from the north 

 and south points each way, from to 90. On the face 

 of the compass are engraved the principal points of the 

 compass. In the centre of the box is fixed a steel pin, 

 on which is poised a delicate magnetic needle, having a 

 jewelled centre. At the side of the compass-box there is 

 a small milled head-screw, by turning which a lever is 

 raised, and the needle lifted from its support ; by this the 

 fineness of the point is preserved when not required for 

 use. Under the lower limb is a socket fitting the conical 

 pin on the upper part of the parallel plates, accurately 

 ground together, and having a true and steady motion 

 when turned thereon. The parallel plates are held to- 

 gether by a ball and socket, and are set firm and parallel 

 to each other by four milled-head screws; these turn in 

 sockets fixed to the upper plate, while their heads press 

 against the lower plate, and being set in pairs opposite 

 each other they act in contrary directions and by this 

 means set up level for observation. Beneath the parallel 

 plates are securely jointed three mahogany legs about 

 four and a half feet long, square at the joint but round 

 below ; these when spread support the instrument at a 

 proper height for use. The lower limb can be fixed in 

 any position by tightening a clamp-screw, which causes a 

 collar to embrace the socket, and prevents its moving, but 



