The total deflection of the galvanometer is satisfactorily constant for all the microphotometer records of the spectra on MC 21648, excepting 3i, which is rejected for a large voltage drop (0.2 volts), producing a reduction of four scale units in total deflection. Spectrum 3i is omitted from further discussion. The quantity _l_ must be corrected for change in _n_, and this may be done by adding to _l_ a quantity equal to the increase in _n_, since the observed change in _n_, which should be constant, corresponds to a shift of the whole spectrum, tending to decrease _l_. The change in _l_, the distance from “clear film” to line center, as measured on the microphotometer tracings, with changing focus, is shown in Table IV. Values of _l_ are corrected. TABLE IV Spectrum 3h 3g 3f 3a 3b 3c 3d 3e Focus 16.6 16.8 17.0 17.2 17.4 17.6 17.8 18.0 _l_ at Hβ 33 36 40 47 49 49 48 43 Hγ 37 38 39 47 47 50 46 47 Hδ 32 35 31 40 41 45 43 40 Hε 24 26 27 33 33 35 37 31 K 42 44 42 50 50 52 54 47 Hζ 12 14 13 19 18 22 24 20 The line depth is the greatest, and the focus presumably the best, where _l_ is smallest. It appears that spectrum 3h is at best focus. Table V contains the values of _m_ for different focus settings, in the same form as Tables III and IV. The quantity _m_ requires no correction for change of _n_. For all the spectra on this plate the K line appears double. The last line of Table V contains the distance, in scale divisions, between the two maxima of the K line on the microphotometer tracing. One scale division corresponds approximately to one Angstrom. TABLE V Spectrum 3h 3g 3f 3a 3b 3c 3d 3e Setting 16.6 16.8 17.0 17.2 17.4 17.6 17.8 18.0 _m_ at Hβ 16 16 14 13 13 12 9 11 Hγ 19 18 18 16 15 14 12 13 Hδ 22 20 20 19 18 17 15 16 Hε 24 22 20 21 22 21 21 19 K 3 3 2 2 2 2 2 2 Hζ 24 23 23 24 25 23 29 28 Width of K 4 4 5 5 7 6.5 9 9 The data of Table V, and the changing width of the K line (thus shown to be an effect of focus) indicate 3h as being the best focussed of the nine spectra. This can also be seen visually from the plate. The focus plate MC 21803 was similarly analyzed and measured. No progressive weakening of the spectra is shown by this plate, and the measures are therefore uncorrected. For the same plate Table VI shows the change of _l_ with focus setting, in the same form as Table IV.