. Carnegie Institution of Washington publication. CHAPTER I. ELLIPTIC INTERFEROMETRY APPLIED TO THE HORIZONTAL PENDULUM. PART I.—DIRECT DIFFERENTIAL REFLECTION. 1. Introduction. Method.—Before using interferences, it seemed inter- esting to apply the interferometer adjustment to the case of simple reflection, the mutual displacement of the two direct images from the front and rear face of the mirror on the pendulum being used for the measurement of the angle of deviation of the pendulum. In such reflection from a glass plate there is necessarily considerable loss of light; but at radii of 20 a
. Carnegie Institution of Washington publication. CHAPTER I. ELLIPTIC INTERFEROMETRY APPLIED TO THE HORIZONTAL PENDULUM. PART I.—DIRECT DIFFERENTIAL REFLECTION. 1. Introduction. Method.—Before using interferences, it seemed inter- esting to apply the interferometer adjustment to the case of simple reflection, the mutual displacement of the two direct images from the front and rear face of the mirror on the pendulum being used for the measurement of the angle of deviation of the pendulum. In such reflection from a glass plate there is necessarily considerable loss of light; but at radii of 20 and 30 meters, when the source of light is a slit closely in front of a Nernst filament, this difficulty is not prohibitive. It is necessary, however, that the lens of the collimator, as well as the plates of glass and mirror used, be of high opti- cal quality; otherwise it is impossible to obtain sharp condensation at a very dis- tant focus. One may also concentrate the slit images to a point by a cylindrical lens, cr ' placed with its linear element at right angles to the direc- tion of the slit. The interesting feature of the method is that it is inde- pendent of any zero-point, as the distance apart of the two images on the far screen at once measures the inclination of the pendulum axis, the normal position being that in which the two images coincide. If the two opaque mirrors are rigidly fixed, the direct or incident beam of light from the source and the subsidiary reflecting mirrors may shift without modifying the datum for the inclination. Further- more, the sensitiveness is twice that of the case of single reflection, other things being equal. The method is thus particularly adapted for the measurement of the inclination of the plumb-bob relatively to the eaith. The annexed diagram, fig. i, will make the method clear. Here s is the fine slit in front of the Nernst filament /, and / the condensing doublet (about 60 cm. focal distance; for rough work an ordinary spect
Size: 1642px × 1521px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorcarnegie, bookcentury1900, bookdecade1900, bookyear1902
