The operation of the instrument described in part I and the interpretation of the results in terms of the amounts of polymerization that occur as a result of photochemical initiation are described. The sensitivity has been independently checked and found to agree with calculation. The usefulness of the instrument is governed by the inherent drift, and, in this application, by the loss of heat from the reaction mixture. These factors impose an upper limit of about 1 min. for the useful time of observation.