. Annual report. Agricultural education. 134 AGRICULTURAL COLLEGE. [Jan. Fig. 2 illustrates this scale as formerly constructed, being divided into 100 equal numbered parts, each numbered part halved by an un- numbered line. Departure point on the new scale is 32. The scale AB can be moved backwards and forwards, and one turn of the micrometer screw moves it just one of these 128 divisions. The drum ef of the micrometer screw is divided into 100 equal parts by lines properly marked and numbered ; each of these 100 parts is divided into 5 equal parts by means of a vernier; hence the four-inch sc
. Annual report. Agricultural education. 134 AGRICULTURAL COLLEGE. [Jan. Fig. 2 illustrates this scale as formerly constructed, being divided into 100 equal numbered parts, each numbered part halved by an un- numbered line. Departure point on the new scale is 32. The scale AB can be moved backwards and forwards, and one turn of the micrometer screw moves it just one of these 128 divisions. The drum ef of the micrometer screw is divided into 100 equal parts by lines properly marked and numbered ; each of these 100 parts is divided into 5 equal parts by means of a vernier; hence the four-inch scale AB is accurately divided into 64,000 equal parts, each part equal to Te^oo of an inch. Linear distances and altitudes are obtained by this instrument, by one and the same operation, with greater precision than by chain, level or any other known means. A level hi (Fig. 1) is fixed on the telescope cc?, so that the axis of the telescope may be placed parallel to the divided scale AB. A magnetic needle having a play of about 15 degrees is also at- tached to the telescope. This serves to check courses. The divided circle M fixed to the common axis O is employed, as in the theodolite, to take vertical angles. To understand the mathematical principle upon which this instru- ment is constructed, the operator requires but a small amount of geometrical knowledge. In Fig. 3, 0 is the centre point of the axis of rotation directly over the divided scale AB; Ob,. " : :. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Massachusetts Agricultural College; Massachusetts Agricultural Experiment Station; Massachusetts Agricultural Experiment Station. Annual report of the Hatch Experiment Station of the Massachusetts Agricultural College. Boston : [s. n. ]
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