1 :','.' v 



The Geodetic Level. 



In response to a request of President T. C. Mendenhall to construct for tin- 

 Worcester Polytechnic Institute a Precise Wye Level, the senior member of this linn 

 iu 189(5 designed and made the type shown on next page. 



The U-ading features are great compactness, rigidity, simplicity of design. 

 manipulation, and thorough adaptation of every part to its purpose, in order to lessen 

 the height above the tripod, the weight of the instrument and the surfaces exposed to 

 wind pressure, this particular form of cradle bar has been adopted; and. while this 

 reduction might have been carried to a greater extent by placing the vertical revolving 

 center inside the tripod head, it was thought not advisable, as sometimes it is desirable 

 to set the instrument on the leveling screws when detached from the tripod. 



As will be seen, the improved tripod is of a very stiff form, which i.> in. 

 where telescopes of great powe-r and highly sensitive spirit levels are used. To eliminate 

 the effect of unequal expansion, the telescope collars are of smallest possible diameter 

 compatible with the diameter of the object glass, and at first were of hardened steel 

 resting on agates at point of contact in wyes. The striding level adopted in plan- of 

 the tixed level is of tubular form and has very short legs. To still further reduce tin- 

 effect of unequal expansion, the substructure, such as cradle bar, fixed bar and other 

 pans, below the agates at point of contact in wyes in this instrument, consisted of steel 

 and iron. Subsequently, however, as the danger of rusting in the field became very 

 apparent, the use of steel and iron was not thought to be as important in portable field 

 inst ruinents when used on tripods as in the stationary ast ronomical instruments ; there- 

 fore we are making the substructure of our customary hard gun-metal, and shall so 

 furnish them, unless ordered to be of steel, in which case the instrument will have to 

 be specially made. (See below.) The same may be said of the hardened steel collars. 

 l"n less ordered otherwise the collars will be made of hardest bell-metal. 



All the parts that must be handled during a field operation are protected by a 

 shield of a non-heat-conducting material. By means of a micrometer screw the telescope 

 can be moved in the vertical plane around the center in the middle of the instrument 

 in order not to disturb the height of the intrument. 



The striding level has a bubble tube reading to 3'' of arc and is provided with an 

 air chamber. Mounted above it is a mirror to enable the observer to read the bubble 

 without stepping aside. Provision is made to readily lock the striding level to the 

 cradle bar, to enable one to use the instrument like an ordinary Wye Level i.with level 

 tixed to the telescope) ; and to carry the instrument on its tripod from station to station. 

 An arrangement is also provided by which the striding level upon reversing will always 

 tind its proper plane on the collars, so as to require but very little attention on the part. 

 of the operator. By means of a clamp screw opposite the micrometer screw the cradle 

 bar can be secured so that the instruments can be used for ordinary wye level work. 



Two auxiliary levels placed at right, angles serve to level up approximately : after 

 which the tinal setting of the striding level is done by the micrometer screw attached 

 to the lixed bar. The vertical center is of hardened steel and runs in a socket of cast, 

 iron. Ail the main parts are either cloth finished or japanned. Tin- beautiful appear- 

 ance of the instrument does not depend upon the external linishing and polishing of 

 parts, but entirely upon the harmony, simplicity and excellence with which the essential 

 feature- of the instrument are designed. 



For a detailed description of the instrument we refer to a paper read by Mr. I)a\ id 



Moli:..r before the Am. SOC. of C. K. (See Proceedings ISil'M'.Mio. 



The telescope is inverting, with an object -lass of 1 < 2 ". focal len-th . 

 and a power of 40 diameters. li is provided with the usual cross ami stadia . 

 In-trument packs in pine wood box. which contains a sunshade, screw driver, adjusting 

 pin and gOBBamei ba-. 



Wright of instrument ....... 14 Ibs. 



Weight of tripod i; ll. 



f iross \\vight of instrument packed securely for shipment in two boxes 7; Ib-,. 

 Price as above, "f brass and bell metal collars. .... S2SO.OO 



Price of i list mmciit, >ult ruclure of steel, a^ above, ext ra. , -.">.()() 



Price of Ingtrument, collars of telescope of hardened steel, extra, . -'">.()0 



Co<l Word for <;odti< i.t-vel of bra>s and bell metal collars Artemisia 



