Vol. 48 creased.'* The predominating effect seems, therefore, to be a "tightening."The suggestion occurs in explanation that possibly the extra electrons when introduced in most cases tend to enter with the other electrons into stable groups or configurations which could not be formed to the same extent without them. SummaryThe apparent heat capacity of electrons, their partial molal heat capacity and the Thomson effect are defined and compared, and the conditions under which they might be numerically equal discussed. The available evidence is examined to determine whether such equality exists in actual cases. It is concluded that for a large majority of the metals studied the apparent heat capacity is not nearly equal to the Thomson effect, and probably not to the partial molal heat capacity. From comparisons of the magnitude of the last quantity with the first, certain tentative conclusions are drawn relating to the specific effects upon interatomic constraints of increasing the negative charge of metals.That the accurate measurement of heats of vaporization is one of considerable difficulty, is evident from the widely divergent values found in the tables of physical constants. The methods available may be divided into two general classes : (1) condensation methods and (2) evaporation methods.-One great difficulty with the condensation method is the correction required for the heat given out by the condensed liquid cooling from the boiling temperature (temperature of condensation in the calorimeter) to the temperature of the calorimeter. This correction involves an accurate knowledge of the specific heats of the liquids used over this range of temperature and such data are no more accurately known than the heats of evaporation which are being measured. The direct evaporation methods, which do not involve such a correction, have a distinct advantage in this respect. Also, since electrical quantities are susceptible of very accurate measurement, the direct method seems preferable. Another great l a Whether these assumed reactions occur entirely in the surface regions of the metals or in the interior is not important from the present standpoint.It should be noted also that other languages, including that of the quantum theory, may be used in describing these results.

Cover-incomparability graphs (C-I graphs, for short) are introduced, whose edge-set is the union of edge-sets of the incomparability and the cover graph of a poset. Posets whose C-I graphs are chordal (resp. distance-hereditary, Ptolemaic) are characterized in terms of forbidden isometric subposets, and a general approach for studying C-I graphs is proposed. Several open problems are also stated.

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