Van Nostrand's engineering magazine . ng 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 rod was read froma vertical arc of two feet radius, whoseerror was eliminated by readings takenin reverse position. Bessels apparatus was similar to Bor-das, with the exception of the device formeasuring the intervals, and the substi-tution of iron and zinc for platinmu and HASE-LINE APPARATUS. 05 .copper The intervals are measured by a tained,and the length of the bas
Van Nostrand's engineering magazine . ng 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 rod was read froma vertical arc of two feet radius, whoseerror was eliminated by readings takenin reverse position. Bessels apparatus was similar to Bor-das, with the exception of the device formeasuring the intervals, and the substi-tution of iron and zinc for platinmu and HASE-LINE APPARATUS. 05 .copper The intervals are measured by a tained,and the length of the base may be represented by an equation of the form scale cut upon a glass wedge, which isintroduced between the bars. The zincstrip carries at each end a horizontalknife edge, and the small strip of ironhas two vertical knife-edges. The dis-tance between the inner of these latter j It may be seen by a comparison that fourand the horizontal knife-edge of the i rods is the least number by means of ii% + avl + /?u9 + yv3 + 6vA 4- a?\ + zinc is measured by inserting the i denote the actual distance meas-ured by the wedge ; then if lx and /2 de-note the length of the strips at the timei is observed, we shall have: i—z-\-7n (x—y); using the notation previously l\ and l\ are the lengths at 62°, ob-tained by comparison with a standard; l\x~l\y h = x-y iyx-y which may be taken to be the length ofthe iron piece at any observation. Bessel used four rods in his measure-ments, each similar to that above de-scribed. Represent the lengths of theiron pieces by L,, , L3, and L4. Letthere be some length s, obtained by acomparison of one of the bars with astandard, and let v,, v3, y3, v4 denotesmall variations of length of the barsfrom 5, so that v^ + v^+ y3 + u4=o. Also let tp t^ tz, t4 be the observedtemperatures, and r,, r9, r3, i\ rates of ex-pansion. Then Li = 5 + yi + ^v It4=8 + v4 + t4r4. From the eight equations obtained bya comparison of the rods inte
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectenginee, bookyear1879
