The formidable mass of accumulated data relating to the optical rotation of camphor and its derivatives suggests at first sight that this field of research has already been exhausted. Closer examination, however, shows that this is far from being the case; on every side supplementary work is necessary, whilst the field itself is so extensive that a vast expanse of fresh ground remains to be broken. The application of the Drude equation by Lowry and his co-workers has resulted in valuable additions to our knowledge of the dispersion measurements of these compounds, but temperature-rotation data and the effects of solvent action are lacking and, with camphor derivatives in general, even if we except the case of camphor itself, these two highly important factors in rotation have either been neglected altogether or accorded no more than a passing consideration. It was in part, therefore, at once the justification and aim in commencing the present work, to repair in some measure this omission and to place on record measurements of these influences which, apart from any resulting theory or generalisation, would have, ipso facto, a real value. In addition, and in this lay the chief incentive to the work, it was believed that investigation of the rotatory power of camphor compounds could scarcely fail to be of interest when referred to characteristic diagrams of the type already studied by Professor Patterson and his colleagues for compounds of a less complex character. Accordingly, in addition to camphor itself, certain of its sulphonic and halogen derivatives have been selected, and examined in such detail as the merits of each case seemed to require
