On the Expansion or Contraction of a Symmetrical Cloud under the Influence of Gravity.

that the longer the wave-length (the lower the frequency) of the exciting radiation, the greater the amount of energy associated with the same photochemical change in the glass. The straight line relation of the data, indicated in figure 2, is suggestive and requires further investigation. This method of portraying the observations is not entirely free from shortcomings. However, if further research substantiates the correctness of the procedure it should prove a useful method of analyzing this type of photochemical reaction. As a final remark it is relevant to note that, in the spectral range investigated, the shortest and the longest wave-lengths have the power of producing the greatest photochemical changes; the former in depreciating, the latter in appreciating the ultra-violet transmission of a soda-lime-silica glass.