While work on the PbS absorption spectrum was in progress, it was noticed that at the highest temperatures used, 1400° C, a spectrum other than that of PbS was obtained. This was immediately attributed to PbO, formed by the dissociation and subsequent oxidation of PbS, and Comparison of the measured wave-lengths with those published by Bloomentahal confirmed this conclusion. The emission spectrum stretches from 3200 to 6700 A and was first analysed by Mecke, Who recognized three by Bloomenthal, Who Showed that the existence of the system which he termed A, B, and C. The spectrum was later remeasured by Bloomenthal, who showed that the existence was of the system C was very doubtful as nearly all the bands belonging to it could be fitted into system B. In addition he discovered a rather fragmentary system D in the ultra-violet. It was considered, therefore, that an investigation of the absorption spectrum besides determining the ground state of the molecule might yield additional data with which to test these analyses. After the present work had been completed, Shawhan and Morgan published an account of the absorption spectrum in which they verify Bloomenthal's analysis. They also classify additional bands into two new systems which they designate C and E, the former not to be confused with the original C system of Mecke, Which is now included in system B. Using temperatures up to 1200° C, they have extended the spectrum to 3000 A and in the present work higher temperatures than this have been, used the spectrum being extended to yet shorter wave-lengths.