138 



The Telescope will be invariably inverting in order to admit of as large an aperture and as high a power 

 as is possible. 'Ihus: its aperture will be \ l inches, the total length i-> atm. it 17 inches, and it will have a 

 magnifying power of 40 diameters. It will be provided with fixed stadia wires, in the proportion of i to 100, 

 the distance to be measured irom a point in front of the objective equal to its focal length. 



The Spirit Level is of the single reading kind, and is generally made so that one division (of ^ of an 

 inch) equals from S to 10 seconds of arc. The sensitiveness of the level will, however, be adapted to the par- 

 ticular requirements. It is not necessary, however, to have it any more sensitive than is required for a fine 

 field instrument, as an over-sensitive level is apt to give more trouble than benefit in its use. 



A Reversion Level of same sensitiveness can be applied instead of the single reading level, if desired, as 

 a convenient (see Reversion Level, p. 134), when the highest precision is not needed. Of course in fine work 

 the reversion level must be used in the direct position as with a single reading level. 



The Auxiliary Striding Levt-1, if one is ordered, is generally made so sensitive that or- division <' 

 of an inch) equals from 8 to 10 seconds of arc; but this sensitiveness t may be made a little greater if desired 

 for exceptional uses only. This latter addition would only be used in the most precise work for the purpose of 

 testing the equality of the collars after protracted use, and when this is done it would be returned to its box 

 (see cut opposite). 



A Metal Mirror will be furnished with the instrument, attachable to either side of the level, enabling the 

 operator to lead the bubble without stepping aside; a convenience which will be appreciated when working on 

 shaky ground. 



Adjust ment. The adjustment of the telescope and the level must be made precisely as in an ordinary 

 wye level, (see adjustment of the wye level, pages 51 and 54 of this hand-book ) The spirit level will be in 

 thorough adjustment when the telescope with its sunshade attached is focttssed for a distance of about ^oa/eet, 

 when the telescope is in perfect balance and the equality of the collars is assured thereby ; for shorter distances, 

 however, there is a small error due to the unbalancing of the telescope caused by the object slide being thrown 

 out. Small as this error may be it can be entirely eliminated by simply bringing the bubble to the ce^er by 

 the use of the micrometer screw. 



Explanation. The foregoing has been written at some length to give a clear understanding of the prin- 

 cipal features of this instrument. Naturally, the question may now present itself, why not use a striding level 

 alone, in place of the fixed or reversion level, as is done in some of the best types of instruments, particularly 

 a%the pivot arms, extending from the middle of the cross-bars, must necessarily be spread quite a distance 

 apart, to readily permit the revolution of the telescope with the fixed level in the wyes. To this we may say, 

 that a fixed level placed below the telescope, where it is guarded against breakage and, in a measure, from the 

 action of the sun, is better adapted to the wants of the Civil Engineer in running quick and accurate levels 

 in cities, towns, etc., than a striding level with its more cumbersome features and manipulations would be, 

 particularly if the work was to be of the most precise character. 



It is only when the collars of a telescope a badly worn or imperfectly made that the striding level has 

 any advantage over a fixed one. As a rule a fix .d level keeps in better adjustment, is simpler to manipulate 

 than the striding level, and is free from the errors due to the uncertainty of contact of the collars and the wyes. 

 Moreover, the construction of the new instrument is such that it has a greater stability than those of previous 

 make. We therefore believe that the fixed level has as legitimate a standing as the striding one. (In this 

 connection read articles on the fixed and striding levels, pages 94 to 98 of this manual.) 



For the above and similar reasons the American Engineers have and will give preference to the instru- 

 ment which has the level fixed to the telescope; and this has led us to the adoption of this feature in our new 

 instruments. This idea is also prevalent among the best instrument makers and engineers in Europe, as may 

 be seen by examining Prof. Nagel's published description of a similar instrument. 



Instrument, Finish, Packing, Weight, etc. The telescope is cloth-finished, 

 while some of the more bulky parts of the instrument are simply treated either with 

 cloth finish or japan, in order to lessen the cost. No attempt will be made to give an 

 elaborate finish at the expense of accuracy and utility ; altogether, as all the other 

 parts will be bronzed and lacquered in a manner customary with us, it will present a 

 handsome appearance. This instrument is packed erect in one box in the same man- 

 ner as we pack the regular engineer's wye level. It is secured to the tripod in the 

 same manner as are all of our instruments with three leveling screws. (See page 134 

 for description ) 



The mahogany box contains a sunshade, wrench, screw-driver and adjusting pin. 



Weight of instrument, 11$ pounds; weight of tripod, 10$ pounds; weight of ma- 

 hogany box, 10$ pounds ; gross weight of instrument complete, securely packed in two 

 boxes for shipment, 60 Ibs. 

 Price of this instrument, inverting telescope, cloth finished, metal 



mirror, fixed stadia wires, and a ningle reading fixed */iirif-l< nl, . $121 ,">.OO 



Extras to Engineers' Precise Level 



Instrument provided with a reversion level (see Reversion Level, page l.'>6), . $20.00 



Instrument provided with 7$ inch auxiliary striding level, in addition to reg- 

 ular fixed level . . . . :'--'. "0 



Center >! in>trmnrnt made of steel, and hardened ami running in a socket of 



cast iron, improved style (Bee cut, page ]'>'>. ..... l~>.<io 



Sunshade with smaller aperture, for use with the telescope when the sun 

 rays are too bright for accurate work, 



(rossamrr lia-:, t protect instrument 



Bottle of fine watch oil for lubricating the centers, etc., 0.26 



: -M work is to he done, a higher sensibility mi^ht he pcrmissable, hut our customary flui.l would he riagffch in 

 such a level, and the hnbhle tube, would have to he filled with pure ether, in order to make it quick artn.. 18. 38). 



An ;ur ch.ui.U-r w.uld t>e necessary to allow for adjustment of ihe bubble, which in this case changes its lenc'h rapidlvfr* 

 slijjh* rhangcs in temperature. By adding a chamher, a feature is introduced which is liable to allect the reli.ibiiitv Of to* 

 spin*, level and entail extra expense. 



Code Word. Kn K iner' Precise Level hut with steel centre Arotliiisu 



