“In 1847 (says Dr. Peacock), I published a series of weights of the human brain, collected at the Royal Infirmary of Edinburgh, together with tables prepared from these observations, together with the much larger number of weights previously recorded by the late Professor John Reid. The observations which follow have been obtained since that time, and though comparatively few in number, yet, as they are not likely to be materially increased and may furnish a useful comparison with the former, I have thought them worthy of being placed on record. The observations on the specific gravity of the brain are entirely new. They were obtained by a different mode from that followed by Dr. Sankey, in his observations of the specific gravity of the healthy brain, and by Dr. Bucknill in his investigation of the density of the brain of insane persons. The former of these observers ascertained the specific gravity of the different portions of the brain, by placing pieces in solution of common salt of different densities; the latter adopted a similar plan, except that he employed solutions of Epsom salts. My own observations were made by first weighing the brain and its several portions in air, and then in distilled water, and calculating the specific gravity by the common formula, viz., as the weight lost by the brain in water is to the weight in air, so is the specific gravity of distilled water (1000) to the weight required.”