134 



Hydrographer's Wye Level. 



With three Leveling Screws. 



Please read : Three leveling screws versus four, p. 38. As regards mode of fastening this instrument to 

 the tripod by means of the center piece or fastener, see cut and description, p. 46, in article " Shifting Center 

 for," &c., also note below. 



This instrument, as shown on opposite page, is exactly similar to our Engineer's 

 18-inch Wye Level (see p. 132), except the telescope, which in this Instrument, is of the 

 inverting kind. Unless otherwise specified, the sensitiveness of the spirit level will be 

 such that one division (^ inch) will correspond to 8 to 10 seconds of arc. 



The weight of this instrument is about the same as that of our 18-inch Wye Level. 

 The box is about 1 inch wider and on this account is about one pound heavier. The 

 tripod legs are spread as far apart at the tripod-head as the leveling screws, in order to 

 ensure the proper degree of stiffness to such an instrument, and on this account the 

 weight of the tripod is increased about 2 Ibs. 



This instrument will be made to Order only. 

 Price, as above, with cloth-finished telescope and level-tube, . . $158.OO 



Extras to Hydrographer's Wye Level. 



Center of instrument made of steel, and hardened ami running in a 



socket of cast iron, improved style (see cut, page 133), . . . 15.00 



Stadia wires, fixed 3.00 



Metal mirror with universal joint. (This is readily attachable to the in- 

 strument and facilitates the reading of the bubble on soft ground 

 without stepping aside 10.00 



Extra sunshade with smaller aperture, for use with the telescope when 



the sun's rays are too bright for accurate work 1.50 



Gossamer water-proof bag, to protect the instrument in case of rain or 



dust 1.00 



Bottle of fine oil to lubricate the level center 0.25 



NOTE. The advantage derived from the use of three leveling screws * in the Engineer's Wye Level, 

 when mounted on a base or circle of larger diameter, consists in the greater ease and precision with which 

 the bubble of a most sensitive spirit-level, and thereby the line of sight, can be controlled, in bench leveling 

 and in work of a very close character. 



This will be more readily understood when we mention that these levels are frequently made to read to 

 single seconds of arc for every one-hundredth part of an inch on the bubble scale, as shown above. 



After an approximate leveling of the instrument, to prevent a change of height of instrument, it is advis- 

 able to clamp one of the leveling screws by its clamp screw at the side, and to level up by the other two 

 screws alone. This should be done in like manner, also, to correct for slight changes in the level caused by 

 the settling of the tripod-legs. 



* Four leveling screws commend themselves in the more ordinary class of instruments for the greater rapidity with 

 which an instrument can lie leveled up *pproximately, and that (no matter how much the leveling screws may be worn) when 

 brought to a true bearing on the lo*er leveling plate, all such looseness is taken up. 



Intermediate base-plate to make the wye level with three leveling screws interchangeable 

 on tripods made for any of our four-screw transits or levels. 



As a connecting link between the instruments with 4 and 3 leveling screws we 

 formerly made an arrangement as shown in side cut on opposite page and described 

 below, and are still prepared to supply it if desired. It, however, seems hardly desir- 

 able to be used, as the greater steadiness of tripod and simplicity and compactness as 

 exemplified by the llydrographer's Wye Level with 3 leveling screws (shown on page 

 opposite) are not attained. While we do not recommend the adoption of this device 

 we retain it as a feature in our manufacture simply to meet the desires that some of 

 our customers may yet have. As can also be seen by referring to the side cut, our 

 Quick Leveling Attachment (see p. 39) may in this case be applied, although it will de- 

 tract still more from the steadiness, and in a measure the advantages of a finer spirit 

 level become lessened. 



With the intermediate base plate arrangement the three leveling screws rest in 

 grooves provided for them in the base, or lower leveling plate. The instrument is at- 

 tached to the tripod by means of a screw in the same manner as the ordinary wye 

 level, inasmuch as the base plate is a part of the instrument proper and is not detach- 

 able. The upper part of this instrument is held firmly in the grooves of the lower 

 base-plate by means of a strong spiral spring in the central socket, which permits the 

 use of the leveling screws for their entire length. The leveling screws of this instru- 

 ment should be kept, as far as possible, in the middle of their run to secure the best 

 action of the spiral spring. 



Price of instrument with this device is the same as above for the regular Hydro- 

 .rrapher's Wye Level. If provided with a Quick Leveling Attachment, 



Price, extra, $8.OO. 



