V. HENRI. Structure des molécules. (Publications de la Société de chimie physique.) Paris. 1925, p. 122.

V. Henri. Structure of Molecules.

The theoretical attempt to approach the study of molecular structure by applying the methods of quantum mechanics ended in failure in the very simplest case, the hydrogen molecule. The cause of this failure lies not so much in the mathematical difficulties of the problem as, apparently, in the inaccuracy of the basic postulates of quantum mechanics. Therefore the study of molecular structure must be pursued by another, indirect route, determined above all by experimental data and then by the most general ideas of quantum and classical theory. Henri’s book is devoted to presenting the results of this indirect study of molecular structure. The book is a transcript of lectures delivered by the author in Paris and does not claim completeness. In the first chapter, using benzene as an example, the chemical methods for determining the structural forms of a molecule are illustrated. Next the concept of the electrical anisotropy of molecules is introduced (the dipoles of Langevin, Debye); the author gives a very valuable summary of data on dipole moments. In connection with the electric moment, the “deformability of ions and atoms” is considered (Born, Geisenberg, Fajans, and other authors).

The results of X-ray spectroscopic studies of the structure of molecules in crystals are considered very briefly. The methods for determining the general character of molecular structure from absorption spectra, on the basis of the quantum theory of spectra, are set forth in the greatest detail.

A special chapter is devoted to continuous, “unquantized” molecular spectra, corresponding, in the author’s opinion, to the transitional state of “predissociation” of the molecule. In conclusion, the author gives a summary of various physical data on the structure of benzene.

Among the significant gaps in the list of methods for determining structure (more precisely, the asymmetry of the molecule), one should note the works of Cabannes, Gans, Raman, and others, which lay the foundations for a new and very convincing method of determining the optical asymmetry of molecules from the degree of polarization of scattered light.

Of course, the listed paths for studying molecular structure can lead only to the most general conclusions, leaving the details unexplained. The way out here must be expected from theory, from the new quantum mechanics.

The book, which to a considerable extent presents the author’s own work and that of his students, in many respects bears an individual stamp. The exposition is extremely simple and clear.

S. Vavilov.