The anthracene structure, which was already partly known, has been investigated in detail. The intensity measurements have been made as accurate and as complete as possible, and a double Fourier analysis carried out for the zones about the three crystallographic axes. From the results of this analysis the details of the structure are deduced. The carbon atoms are found to lie quite accurately at the corners of three regular plane hexagons, the distance from centre to centre being 1.41 A.U. This molecule is, however, inclined at varying angles to all the crystallographic axes. These angles have been determined, and the structure is completely defined, by a statement of the direction cosines of the long and the cross axes of the molecule which are given on p. 78-79. The 21 parameters of the structure have been determined from the analysis and are given on p. 80. All the carbon atoms in the molecule except one are resolved as circular masses in one or other of the projections. The closest distance of approach between atoms in adjacent molecules is about 3.67 A.U., in marked contrast to the distance of 1.41 A.U. between the atoms within the molecule. The peak values of the electron density are highest for the carbon atoms in the meso- positions, and fall off a little in the end benzene rings. This effect is accompanied by a slight broadening of the structure, and may be connected with the chemical difference between the meso- and benz- positions, or with thermal agitation. The electron count is in good agreement with the chemical structure, showing a minimum value at the tertiary carbon centres
