LEVEL. 



j/ecting from it diametrically opposite to fast, but admits of a slight movement, 

 each other. H is a small brass angle, or either way, when acted upon by the mill- 

 frame, called a Y, screwed to the end of headed screw m. 



the arm C : it supports in its forked ter- Our readers will readily perceive the 

 ruination one end of the telescope K, of simplicity of this level, beyond any others 

 which the other end rests in a Y, (letter- in use ; and will lament the demise of a 

 ed N), similar to II, but which can be gentleman, who,, to profound theory, 

 raised or lowered, by means of a screw .added the -most ingenious and skilful prac- 

 having a milled head ; as seen at ?/. The tice. 



spirit level L is fixed to the telescope by Where a very long and continued 

 two screws at its ends, whereby it can be range of brickwork is to be raised, it is 

 brought into exact adjustment with the often advisable to use a water level, made 

 culmination of the telescope. by laying a ridge of mortar along the 



The level, which is the essential part centre of the wall, and opening a very 

 of the instrument, has been already de- narrow channel throughout its centre 

 scribed; but it is proper to add, that the longitudinally, so as to form a kind of 

 ends of the tube containing the alcohol, trough; let the ends be stopped, and the 

 when made of glass, should be hermeti- trough be filled with water, as far as it 

 cally sealed at its ends, which should then will flow. The surface of the water will 

 be cased in brass. Mr. Ram sden prefer- give a true horizontal level; which, if 

 red a very slight convexity in the tube ; continued for miles, would conform ex- 

 considering it best adapted for shewing actly to the curvature of our globe. To 

 the most trifling deviation from a perfect continue the level along the rest of the 

 level, and causing the bubble to become trough, stop it at the place where the wa- 

 more accurately centrical. With respect ter reached, and raising the adjacent part 

 to the telescope, it is similar to those ge- with more mortar, let the trough of the su- 

 nerally fitted to theodolites, &c. and has perior level be filled, and thus in succes- 

 been described in the preceding part of sion. The difference between the end 

 this article. It is laid on in the two Y of one trough, and the beginning of an- 

 pieces, and kept in by two curved pieces other, will shew the respective levels; 

 of brass. In figure "h is the achromatic from which parallels may be set off at any 

 object glass, fixed within the end of a height above by plumb lines of equal 

 tube, sliding within the external cylinder length. This mode is often practised in 

 of the telescope, and moved very gra- large works, such as fortifications, and 

 dually by a rack and pinion on the mill- when strata of masonry are to be regu- 

 headed nut i : the distance of the glass h larly disposed ; also to prevent those ir- 

 from the eye-piece, is thereby adjusted regular breaks, and partial connexions, 

 to a suitable focus. that are almost inevitable where small sal- 



The eye-piece K contains two lenses, lows, or triangular levels, with plumb 

 sliding in a tube fixed to the telescope, weights, are in use. 



for adjusting them to a distinct vision of When no instrument can be obtained, 

 the cross wires, or hairs, which are held and where it is not easy to draw an exact 

 in a proper state of tension in the frame level by the foregoing means, take the 

 /, and regulated to the axis, or line of hose of an engine, and having fixed one 

 sight, by four minute screws passing endat the spot whose level is to be sought, 

 through the outside of the telescope. (on any opposite bank, for instance,) car- 



We have before shown how the four ry the other end to the place where the 

 screws act upon the two parallel plates, corresponding height is to be established, 

 a a and e e, while the axis b can be set Fill the hose with water until it ceases to 

 very nearly perpendicular; then by the require raising at the further end. When 

 screw y the telescope can be set very both ends show full to the brim, and that 

 nearly level. To turn the telescope about the water is retained at both, then they 

 horizontally upon its axis /, a screw m are on the same level : for it is a maxim 

 works in a fixed collar i> ; its nut p is in HYDROSTATICS (which see), that water, 

 lastened upon an arm which projects or, indeed, any fluid heavier than atmos- 

 from a clamp g, embracing a collar upon pheric air, will, when at liberty, always 

 the axis /, and is tightened by a screw r ; find its own level. 



which being unscrewed, the clamp Where a succession of contiguous le~ 

 springs open, and the telescope, together vels are wanted, it will often be found 

 with the level, moves round with freedom convenient to use a small leaden pipe, of 

 upon the axis I, according to the pleasure about half an inch bore, which should be 

 of the operator. When the screw 7* is applied as above described ; or even a 

 tightened, the clamp holds the telescope common gutter, made of two pieces of 



