. The London, Edinburgh and Dublin philosophical magazine and journal of science. obtained for a hook having an outer radius of 0*75 in. andan inner radius of 0277 in., the plate being 0*123 The effect thus produced is equivalent to superposing ablack cross upon the interference colours produced by thestress, and it serves a useful purpose in that it enables curvesof principal stress to be drawn graphically, or by calculation Optical Determination of Stress* 749 when these loci are determined with reference to the angularpositions of the nicols. Snch curves have been determinedgraphi
. The London, Edinburgh and Dublin philosophical magazine and journal of science. obtained for a hook having an outer radius of 0*75 in. andan inner radius of 0277 in., the plate being 0*123 The effect thus produced is equivalent to superposing ablack cross upon the interference colours produced by thestress, and it serves a useful purpose in that it enables curvesof principal stress to be drawn graphically, or by calculation Optical Determination of Stress* 749 when these loci are determined with reference to the angularpositions of the nicols. Snch curves have been determinedgraphically in this case and are shown by fig. For measurement of the stress it is necessary to get ridof the distorting effect produced by the black cross, and I amgreatly indebted to Professor Silvanus Thompson, ,for suggesting for this purpose the use of two quarter wave-plates (H, I, tig. 1) set with their axes inclined at 45° to theNicols prisms, whereby the plane wave issuing from the firstnicol B is converted into circularly polarized light. Thecircularly polarized beam produced by this combination,whether right-handed or left-handed, has no special directionof polarization, aud it therefore presents the same aspect toall parts of the object under stress. It is again convertedto plane-polarized light by the inverse combination of quarterwave-plate and nicol and the interference fringes are stillproduced, while the black cross disappears. This arrange-ment has the further practical advantage that, except for aslight and invariable change of tint, the interference coloursproduced are independent of the angular position
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectscience, bookyear1840
