=The Physics of Smell.=--The principal subject of Prof. W. E. Ayrton's vice-presidential address on physics at the British Association was the physics of smell, which was presented as a subject that had been but little studied. In testing the generally accepted idea that metals have smell, based on the fact that a smell is perceived with most of the commercial metals when handled, the author had observed that when these metals were cleaned or made outwardly pure the smell disappeared. Yet it is shown that these metals acquire smells when they are handled or abraded by friction, which are characteristic and serve to distinguish them. This may be ascribed to chemical action, but not all chemical action in which metals may take part produces smell; for when they are rubbed with soda or with sugar no smell but that of soda or of sugar is perceived; nor is the metallic smell observed when dilute nitric acid is rubbed on certain metals, though the chemical action is very marked with some. But mere breathing on certain metals, even when they have been rendered practically odorless by cleaning, produces a very distinct smell, as also does touching them with the tongue. These smells have hitherto been attributed to the metals themselves, but Professor Ayrton looks for their source in the evolution of hydrogen, which carries with it impurities, hydrocarbons, especially paraffin, and "it is probable that no metallic particles, even in the form of vapor, reach the nose or even leave the metal. While smells usually appear to be diffused with great velocity, experiments prove that when the space through which they have to pass is free from draughts their progress is very slow, and it would therefore appear that the passage of a smell is far more due to the actual motion of the air containing it than to the diffusion of the odoriferous substance through the air." The power of a smell to cling to a substance does not appear to depend on its intensity or on the ease with which it travels through a closed space. Experiments to determine whether smells could pass through glass by transpiration either revealed flaws in the glass or ended in the breaking of the very thin bulbs and gave no answer.