. Carnegie Institution of Washington publication. THE AID OF THE ACHROMATIC FRINGES. 63 The low value of E when the smaller pressures are applied is again the result of irregular or insufficient contact of the rod with the abutment of the apparatus. Much greater pressures are apparently needed to secure an adequately fixed seat of so rigid a body as the brass rod. 33. The same. Glass. — Glass rods of about the same size as the sheath were next tried, the dimensions being L = cm. 2r = o-36 cm. .A= Observations were made in triplets for loads between and kg. The following re
. Carnegie Institution of Washington publication. THE AID OF THE ACHROMATIC FRINGES. 63 The low value of E when the smaller pressures are applied is again the result of irregular or insufficient contact of the rod with the abutment of the apparatus. Much greater pressures are apparently needed to secure an adequately fixed seat of so rigid a body as the brass rod. 33. The same. Glass. — Glass rods of about the same size as the sheath were next tried, the dimensions being L = cm. 2r = o-36 cm. .A= Observations were made in triplets for loads between and kg. The following results are examples: 70 75 65 69 69 cm. io~lljE= A film of pitch was then placed between the end of the glass rod and the cast-iron abutment. The apparatus was heavily loaded for some time to squeeze out all superfluous cement. The triplets measured between and kg. of load showed the same order of value, viz, io5AJV/AP = 77 70 72 69 65 65 cm. io~n£= i-5 I-5 The results throughout in very different adjustments are thus remark- ably consistent, but they are all enormously too low, probably not more than about one-third to one-quarter of the true value of E. These unsatisfactory results were not expected, because the modulus is only about half that of brass. The sec- tional distribution of stress is thus even less uniform in case of glass. Experiments were also made in cycles, but the early results, though markedly looped, were not quite trust- worthy. The following values are of later date and better, remembering that the micrometer reads to but io~4 cm. :. = o. ioBAAT= o 130 285 345 440 53° 475 373 335 *55 20 cm. They are given in figure 44 and show both in the curved loci and irregularity of detail, that the true elastics of the glass are masked by the incidental discrepancies. The values of E thus obtained for glass, though consistent, are necessarily too small. It appears, therefo
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