During the year 1874—5, in association with the late Professor Tait, a research was undertaken which involved the production of very perfect vacua, and with the object of improving on the then known methods, dense charcoal was employed as an efficient absorbent of traces of any gaseous residuum. An account of these experiments communicated to the Royal Society of Edinburgh appeared in ‘Nature,’ July 15, 1875, under the title of “ Charcoal Vacua.”