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C. L. Berber & Sons' Universal Level Trier. 



A most valuable and indispensable Apparatus for testing the sensitiveness and regularity 

 of curvature of Spirit Levels used in Engineers' Field Instruments, etc., etc. 



Introduction The Spirit Level, occupying, next to the graduations and tele- 

 scopic measurements, so important a place on the Instruments of Precision used in 

 Geodesy and for Scientific Research, it is absolutely necessary for those using such 

 instruments to know the sensitiveness of a level as expressed in seconds of arc, and, 

 whether it has been ground to a true curvature as indicated by a uniform run of the 

 bubble, both of which are necessary in order to arrive at correct results in the use of 

 instruments. To fully understand this we refer the reader to the various articles on 

 this subject printed in our Handbook, notably those on pages 7,38, 102 and 103. As the 

 Engineer, Surveyor or Scientific Investigator lias frequently no means of testing 

 the character of these levels, we, as a rule, determine it, or its mean value, and 

 send a statement, to this effect, with every important instrument issued by us. 

 Indeed, so necessary is it to know the mean value of Spirit Levels, that many of the 

 larger Schools of Civil Engineering, Physical Laboratories and Astronomical Observ- 

 atories have been supplied by us with this apparatus for the acquirement of this knowl- 

 edge so that the student might understand better the character of his instruments. 

 However, as a more universal application of this apparatus is desirable at the centers 

 of learning, and as there seems to be a growing demand for a simple, cheap and ready 

 device, we have improved our ordinary apparatus and are now prepared to furnish the 

 above-mentioned Universal Level Trier. By a more extended use of this apparatus at 

 such schools we hope, in time, to abate the reprehensible practice of using spirit levels 

 that are unfit for the character of an Instrument. We have seen cases where the more 

 ordinary Engineers' Transits were provided with front plate-levels which would hardly 

 indicate five minutes of arc in an instrument reading to thirty seconds. With such an 

 instrument the plane of motion of the line of collimation cannot therefore be controlled 

 within five minutes of arc, from a true vertical plane, and all horizontal angles measured 

 by it are influenced by the uncertainty arising from this defect. 



Description. The Level Trier as designed and made by us is exceedingly simple 

 and of a more universal character than any we have seen before, and it is especially 

 adapted to the wants of Engineering Schools and Laboratories. It consists of an iron 

 base plate, upon which is mounted an iron bar having at one end two pivotal centers 

 resting in receptacles provided for them in the base plate, and at the other end a micro- 

 meter screw carrying a disk graduated into 100 parts. 



The bar is provided with fixed wyes in which levels to be tested may be placed, 

 also suitable scales are attached ; when the latter are not needed they may be turned 

 back out of the way. At the pivotal end means are provided for supporting an 

 entire instrument or the parts containing the levels to be examined. An adjustable 

 fork is provided at the right end, which serves to steady the telescope when a wye level 

 bubble is to be examined. If a plate, box, or telescope level of an instrument having 

 three leveling screws is to be tested, the latter may be placed in the grooves provided 

 for them, but if an instrument has four leveling screws a special plate can be attached 

 so as to raise it above the wyes on the bar. The points of the pivots and micrometer 

 screw are hardened, and the latter bears on the base plate on a hardened and polished 

 surface. This bearing is often made movable excentrically with regard to the screw 

 point, so that the point of bearing can be changed in case of wear so as to always present 

 a smooth surface. The arm is about 18 inches long and the pitch of the micrometer 

 screw one-sixtieth of an inch. The cut will give a clear idea as to the arrangements of 

 the parts and the positions to be occupied by the specimens to be tested. 



Mounting". The best place to mount the apparatus is upon a solid masonry 

 shelf built into a wall at a convenient height (so that the operator can be in a sitting 

 position), or upon a window sill where direct contact can be made with the stone. A 



