. Carnegie Institution of Washington publication. REVERSED AND NON-REVERSED SPECTRA. 157 In figure 97, GG' and HH' are double slides like the carriage bed of a lathe, each about to 2 meters long and 10 cm. wide, rigidly fastened together. They are placed at right angles to each other on a fiat table, the vacant distance between G' and HH' being less than a meter. For ordinary purposes they need not be screwed down. A, B, D, K, are flat carriages, or tables, provided with screw sockets for supporting the different standards, and capable of sliding to and fro with a minimum of friction. A ca
. Carnegie Institution of Washington publication. REVERSED AND NON-REVERSED SPECTRA. 157 In figure 97, GG' and HH' are double slides like the carriage bed of a lathe, each about to 2 meters long and 10 cm. wide, rigidly fastened together. They are placed at right angles to each other on a fiat table, the vacant distance between G' and HH' being less than a meter. For ordinary purposes they need not be screwed down. A, B, D, K, are flat carriages, or tables, provided with screw sockets for supporting the different standards, and capable of sliding to and fro with a minimum of friction. A carries the micrometer slit S. B and C are joined by the Rowland rail R, whose length is thus equal to the radius of the concave grating to be examined, or nearly so, so that the ends of R are on vertical axes at b and d. B also supports the table C (somewhat enlarged in the side elevation, fig. 98), on which the table t of the grating g may be adjusted on its leveling screws. To secure a common axis, 6, e, the rod at ace is twice bent at right angles. Moreover, if c is turned to one side, the supporting rod e may be screwed into the vacant socket b at the end of R. For the case of fig- ure 98, the angle of diffraction 6 is varied and \ = D sin 6, where D is the grat- ing space. For the other case (c being turned aside and C screwed into and turning with b) the angle of incidence is varied and X = D sin i. This is much simpler in form than the early method 97 Finally, the table C carries the essentially new addition to the apparatus (shown in front elevation in fig. 99), viz, the long slot ff, adapted to support the right-angled reflecting prism E and at the same time to allow free play to the rail R within ./f. Figure 99 then shows the progress of the rays (turned 90° to the front in a horizontal plane) from the slit or collimator, 5. They are doubly reflected at E, return in a vertical plane and then impinge on the grat- ing at G. The rays thereafter pass along the rail
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