100 Description of a Portable Levelling Instrument 



heavy for easy transport. The level represented in the ac- 

 companying drawing (Plate 1st), vi^as designed to supply this 

 want. It consists of an accurate spirit-level, a 10-inch tele- 

 scope, and a compass, so arranged as to admit of being very 

 portable. The telescope unscrews at letter A, so as to form 

 two compartments, and the whole is packed in a pocket case 

 measuring 6 by 2| inches ; and the tripod on which it stands 

 does not exceed the bulk of a thick walking staff. 



Referring to the drawing, B C is the level, D a circular 

 level, E the compass, F screw for adjusting focus, G the eye 

 piece, H screw acting on spring K L, which is fixed to the 

 telescope at M by a crutch on which it moves, N the screw 

 by which it is fixed to the tripod, O P Q R the top of the 

 tripod, which contains a ball and socket-joint, shewn in dotted 

 lines, which can be clamped and undamped by means of a 

 screw viTought on the inside of the part S T. In setting the 

 instrument, the screw S T is first undamped, and the instru- 

 ment is moved by the hand on the ball and socket-joint until 

 the air-bubble of the level D occupies the centre of the 

 circular box containing it. The screw S T is then clamped, 

 and the instrument being directed to the object to be ob-< 

 served, the final and more perfect adjustment is made by 

 bringing the air-bubble B C to occupy the centre of its tube, 

 which is done by means of the screw H, which acts on the 

 spring K L. The tripod is that used by Dollond for the 

 camera lucida, and answers both instruments. The tele- 

 scope can be made either, as in ordinary levels, to reverse 

 the objects, or, as in theodolites, to shew them in their true 

 positions. In this level made for myself, I have adopted 

 the latter construction, in order that the instrument may an- 

 swer more perfectly the purposes of a field telescope. The 

 addition of the compass is ?ilso a further convenience. 



In connection with this instrument, I have also had a port- 

 able levelling staif made, which also is shewn in Plate I. It 

 consists of an elliptically-moulded staff, 3 ft. 3 in. in length, and 

 cut through the middle ; the two halves are hinged at one ex- 

 tremity, and when unfolded, are fixed by a spring at A, form- 

 ing a rod 6 ft. 6 in. long, on the flat side of which the gradua- 

 tions of feet and inches are painted ; when closed, the gradua- 



