The Astrophysical journal . rference apparatus is required. We propose to give a brief account of a part of the investi-gations which we have made for the purjjose of solving the vari-ous problems just enumerated, emplo^ing an interference appa-ratus having special properties which will be described at theoutset. I. FRINGES FROM SILVERED PL.\TES. The ordinary forms of interference apparatus divide eachincident wave into two waves capable of interfering. Each point The radiations employed up to the present time, excepting the red line uf cad-mium, are not single, but are composed of several clo
The Astrophysical journal . rference apparatus is required. We propose to give a brief account of a part of the investi-gations which we have made for the purjjose of solving the vari-ous problems just enumerated, emplo^ing an interference appa-ratus having special properties which will be described at theoutset. I. FRINGES FROM SILVERED PL.\TES. The ordinary forms of interference apparatus divide eachincident wave into two waves capable of interfering. Each point The radiations employed up to the present time, excepting the red line uf cad-mium, are not single, but are composed of several closely grouped lines, one of whichis much brighter than the rest; the numbers given for the wave-lengths refer to thesepredominant lines. APPLICATIONS OF INTERFERENCE METHODS 89 in the focal plane of the observing telescope — the imaginaryobservation screen — thus receives, from each point of the light-source, two vibratory motions having a difference of path order that the phenomenon may be distinct, it is necessary. 0 7. 03 014 0-5 Ob 07 o« 0.^ Fig. I. that A have a single value at every point of the screen, i. e., thatevery pair of waves reaching a given point have the same differ-ence of path. Supposing this conditio7i of perfect distinctness to besatisfied, the luminous intensity will vary from one point toanother in the focal plane; it is a function of A alone: thecurves of equal luminosity are represented by the general equa-tion A = a constant. The maxima are defined by A^AX, and the minima by A = AA. -|—, X being the wave-length of the light employed and K 2^ whole number. If we suppose that the twointerfering waves have the same intensity (as is ordinarily thecase), the minima are zero; the curve which gives the luminousintensity / as a function of A is a sinusoid (Fig. i, curve A).The fringes consequently have the appearance of bright bands,separated by dark bands with ill-defined edges; the passagefrom maximum brightness to the neighboring minimum is grad-
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectspectru, bookyear1895
