APPENDIX. 



SOME METHODS, NOT ALREADY EXPLAINED, FOR ADJUSTING THE INSTRU- 

 MENTS ENUMERATED IN THIS CATALOGUE. 



We feel that we owe an apology to our readers for the imperfect arrangement of our hand-book and 

 illustrated catalogue. This has been caused by its gradual enlargement as our business has increased. It is 

 our intention, should other pressing duties permit, to rearrange the descriptive part of the catalogue after the 

 completion of several new types of instruments which are now contemplated, and to bring into their proper 

 order the various topics treated in this book. C. L. B. 



Spirit-Levels on Metal Base. (See page 127.) 



A level plane surface is required, upon which the adjustment of a level, mounted 

 on a plane metal base, may be made. Such a level surface may be some portion of a 

 field instrument, as the horizontal plate of a transit or the bar of a wye-level, which 

 may be made horizontal by the leveling screws. If an instrument is not available, a 

 plane surface upon any piece of machinery which may be suitably raised or lowered, 

 may be used. 



Place the level upon the plane surface with its edge coinciding with a straight line 

 previously marked upon the surface, and bring the bubble to the center of the graduated 

 lines or marks ruled on the glass tube, by raising or depressing the plane surface. Next 

 reverse the level end for end, taking care to replace it precisely in the place that it 

 previously occupied, and notice whether the bubble returns to the center of the gradua- 

 tions ; if so, the level is in adjustment ; if not, correct one-half the error by means of the 

 two opposing nuts, or by a capstan-headed screw, provided at one of its ends, and cor- 

 rect the other half by raising or lowering the plane surface. Repeat these operations 

 until the adjustment is perfect. 



Locke's Hand-Level. (See page 127.) 



There are several methods by which this instrument may be adjusted, (a) Select 

 a sheet of water with an unobstructed view of not less than 200 feet, and sight through 

 the level at an object whose height above the water has been made the same as the 

 height of the eye. If the bubble is bisected at the same time that the object is bisected 

 by the horizontal wire, the level is in adjustment ; if not, move the frame containing the 

 wire, by means of the screw or screws placed at the ends of the mounting of the level, 

 until this is the case. (&) If an adjusted wye-level is at hand, set it on its tripod at a 

 height corresponding to the height of the eye above the ground, and direct it at some 

 well-defined object of suitable size, as the target of a leveling rod, distant about 500 feet, 

 and in the level plane given by the instrument. Now raise the hand-level to the eye 

 and notice whether its wire bisects both the object and the bubble at the same time. 

 If not, adjust the wire as explained above, (c) Select a tolerably level place where 

 there are two trees, about 200 feet apart (two telegraph posts or two sticks fastened to 

 a fence will answer the purpose). Find, by pacing or otherwise, the point midway 

 between the two objects selected. Standing at this point, raise the hand-level to the 

 eye, sight at each object in succession, and make distinct marks where the wire inter- 

 sects them when the bubble is bisected. These two points will be approximately in 

 a level line, although the instrument may be out of adjustment. Walking to the 

 side of either of these objects, place the hand-level against the mark upon it and sight 

 at the mark upon the other object. If the bubble is then bisected by the horizontal 

 wire the level is in adjustment ; if not, adjust it as above. 



Hand-Level and Clinometer. (See page 127. ) 



If the instrument is of the style shown in the cut, it may be adjusted thus. Clamp 

 the index or vernier of the arc at and test the adjustment by the methods described 

 for Locke's hand-level. If the bubble is not bisected by the wire, the level must be ad- 

 justed by raising or lowering the tube containing it by means of one of the adjusting 

 screws at the end ; or in some instruments by moving in or out a square tube to which 

 the wire is fastened until the adjustment is made. This latter tube should then be 

 fastened by a screw or marked by a scratch, as the case may be. 



If the style of the instrument permits of being placed with its base upon a plane sur- 

 face, as is usual with an ordinary clinometer, the parallelism of the level with the base 

 should be tested, when the index is at 0, by the method explained above for adjusting 

 the spirit-level with the metal base. If found to be out, the spirit-level should be ad- 

 justed by one of the adjusting screws at the end of its tube. The line of sight must 

 now be verified as explained for the hand-level. If found to be out, the adjustment 

 must be made by moving in or out the square tube carrying the wire as described above. 



