. Carnegie Institution of Washington publication. 138 DISPLACEMENT INTERFEROMETRY APPLIED TO A resilient, straight bronze wire, 21=22 cm. long, was selected for the purpose, mm. in diameter and weighing gram per centimeter. This was trussed (fig. 175), at about one-fifth of the length from the end of the needle by a thinner brass wire, stretched from the top of the hanger and mirror sup- port. As the truss was not sufficiently stiff, laterally, to support the two shots, (m = gram each), it had to be strengthened by a thin glass stem mm. in diameter and 14 cm. long. This
. Carnegie Institution of Washington publication. 138 DISPLACEMENT INTERFEROMETRY APPLIED TO A resilient, straight bronze wire, 21=22 cm. long, was selected for the purpose, mm. in diameter and weighing gram per centimeter. This was trussed (fig. 175), at about one-fifth of the length from the end of the needle by a thinner brass wire, stretched from the top of the hanger and mirror sup- port. As the truss was not sufficiently stiff, laterally, to support the two shots, (m = gram each), it had to be strengthened by a thin glass stem mm. in diameter and 14 cm. long. This was tied on at its ends with fine silk thread. and a little wax. Hence the stem would offer no appreciable purchase to the radiant forces except (unavoidably) at the shot, which were about mm. in diameter. The results showed that the limit had already been reached in the preceding needle, so far as the stem is concerned. The constants* of the apparatus were thus M = 949 grams. m = gram. ^ = cm. /= L = 26icm. Tested by a small sphere (ball-bearing, diameter c"1-. mass 1-0415 grams) of moment of inertia TV = , the slightly modified quartz torsion- fiber showed a period of T = seconds. This, in the equation, § 101, makes 7 = io~7Xi-735 Ay Ay0 = cm. The same result was obtained with the needle itself vibrating in vacua. The moment of inertia was here TV = , to which per cent were to be added to allow for the accessories (wire truss, hanger, and mirror). The period found was T = 3i3 seconds. This in the equation gives 7 = io~ Ay, or Ay0 = cm. In fact, it seems to me that with care as to the increments of N contributed by the parts of needle, this method is preferable, in spite of the tediousness of finding the long period. *R and / were found by measurement with a distant telescope and a scale near Please note that these images are extracted from scanned page images that may have been digitally enhanced f
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