training set but the other 428 spectra also. This is not called predictive ability because of the selection process employed in the training. However, the 126 spectra which participated in training are completely representative of the overall data set with regard to the question of oxygen presence-absence. By going through a feature selection routine identical to those described above, the number of mfe positions used in these 126 spectra can be reduced to 104, and the number of spectra
used to 114. Thus, the entire data set of 600 spectra of 132 m/e positions (600 X 132 = 79,200) can be completely represented by 114spectraof 104peaks (144 x 104 = 11,856), a substantial savings,
RECEIVED for review June 26, 1970. Accepted October 19,
1970.
Double Beam Photon Counting Photometer with Dead Time Compensation K. C. Ash1 and E. H. Piepmeier Department of Chemistry, Oregon State University, Corvailis, Ore. 97331 A low cost double beam photon counting photometer has been built with integrated circuits. The improved regulation of the double beam instrument is compared to single beam operation of one of its beams, and the limitations of double beam compensation are discussed. The counting precision due to shot noise for the double beam instrument compared to that of a similar single beam instrument is found to be worse by a factor of
