Van Nostrand's engineering magazine . avorable that itwas decided to take advantage of it inmeasuring the great arc, which extendsfrom Ismail, near the mouth of the Dan-ube, to the northern boundary ofSweden, a distance of 1,800 miles, andcorresponding to 25° 20 of arc. Thetask was completed in thirty-six required the measurement of 10bases; the determination of latitude at13 points ; and the location of 275 prin-cipal stations. Struve invented a base-line apparatus,which may be briefly described as fol-lows. It consists of a single bar of irontwo toises long, terminated at one ex-tre
Van Nostrand's engineering magazine . avorable that itwas decided to take advantage of it inmeasuring the great arc, which extendsfrom Ismail, near the mouth of the Dan-ube, to the northern boundary ofSweden, a distance of 1,800 miles, andcorresponding to 25° 20 of arc. Thetask was completed in thirty-six required the measurement of 10bases; the determination of latitude at13 points ; and the location of 275 prin-cipal stations. Struve invented a base-line apparatus,which may be briefly described as fol-lows. It consists of a single bar of irontwo toises long, terminated at one ex-tremity by a small cylinder, while to theother extremity is affixed a lever, knownas the lever of contact. The end of theshort arm of this lever is spherical inform ; the longer carries an index movingin front of a graduated arc attached to the bar. The reading of the arc indi-cates the length of the bar as found byobservation. The lever, being placed incontact with the forward bar, is main-tained in position by a spring attached to the lever. A pair of thermometerslying in the bar indicate its bar is wrapped with cotton and clothto guard against rapid changes of tem-perature. In the geodetical operations of De-lambre, executed under the direction ofthe French Academy, Bordas apparatuswas employed. Each rod consisted of aplatinum strip two toises long, uponwhich lay a copper strip, free to expandin one direction only. The copper stripbeing somewhat the shorter, served as ameasurer of the platinum strip. In prac-tice this was effected by means of a scaleengraved upon the copper, which wasread by a vernier on the platinum. Fromthis reading the length of the platinumstrip was calculated. At the extremityof the platinum strip was a smaller pieceof the same material, sliding in a groovecut in the larger strip, and having *uponit a vernier, which served to measure thedistance between successive bars. Bothverniers were read by inclination of the ro
Size: 875px × 2858px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, booksubjectenginee, bookyear1879
