MECHANICS AND USEFUL ARTS. 65 



is toothed upon a portion of its circumference. On each side of this 

 wheel is a rack, attached to a piston, which is made to fit tightly into 

 a cylinder by a cap-leather. In the under side of the cylinder is an- 

 other valve communicating with an exhausting chamber, and on each 

 side of the racks are guides for the piston. The teeth of the wheel 

 are made to take in either of the toothed racks according as the door 

 is opened one way or the other, so that, the piston will be drawn along 

 the cylinder, leaving a vacuum behind, at a uniform and regular de- 

 gree of resistance, until the door is released, when the unbalanced 

 pressure of air upon the face of the piston will cause the door to re- 

 sume its original position. The use of the valve communicating with 

 the outside of the cylinder is that, in case of a leakage of air behind 

 the piston, it shall be driven by the return of the piston through it to 

 the outside. The use of the exhausting chamber and valve communi- 

 cating with it is, that a portion of the leakage air or oil, which cannot 

 be discharged by the valve leading outwards, escapes into the exhaust- 

 ing chamber, which allows the piston to get to the bottom, and to 

 bring the teeth of the rack in hard contact with those of the wheel, 

 and thereby keep the door steady and in its proper place when shut. 

 The box requires to be filled with lard or sperm oil to seal the piston, 

 and keep the whole lubricated. Civil Engineer and Architect's Jour- 

 nal, May, 



THE OROGKAPH. 



PROF. LOCKE, of Cincinnati, in a letter to the Boston Journal, de- 

 scribes a new instrument with the above name, which, if it proves to 

 be all that is claimed for it, will be of great value to the engineer. 

 The great object to be attained in making a survey for a road is to 

 draw upon paper, to a determinate scale, the profile of the line of sur- 

 vey, from which correct, estimates can be made of the amount of exca- 

 vation and embankment, &c., necessary for the construction of the road. 

 This profile represents the distances of prominent points and their rel- 

 ative heights or differences of height. The data required to make 

 this profile are, at present, obtained only by a very slow and laborious 

 process, calling for a great degree of skill and science on the part of 

 the principal operators, besides the services of several assistants. To 

 reduce to paper the results of these labors becomes also a very tedious 

 undertaking. By this instrument, the profile is drawn accurately 

 upon a web or fillet of paper during the progress of the survey. A 

 carriage is mounted upon wheels accurately made, the revolutions of 

 which, when drawn over the ground, determine precisely the surface 

 measure or travelled distance, as is done by the well-known perambu- 

 lator or circumferentor. This distance is registered by one part of 

 the mechanism when required. A fillet of paper is drawn along under 

 a stationary pencil or pen, by means of wheelwork, set in motion by the 

 revolution of the carriage-wheels. The velocity of the last wheel in 

 this train is regulated by means of friction face-wheels, having plain and 

 smooth surfaces, which have their relative diameters increased or dimin- 

 ished bv the movements of a mercurial level and floats, or a pendulum, 



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