Experiments with Lord Kelvin's recorder show that variations in the electrical state of the atmosphere precede a change of weather. Then, with a very large voltaic battery, a tremendous quantity of electricity could be poured into the atmosphere, and its electrical condition could be certainly disturbed. If this could be made practically available, how useful it would be to farmers when the crops were suffering from excessive drought! It might be more powerfully available than the imagined condensation of a cloud into rain by the reverberation caused by the firing of a range of cannon. But what is the practical benefit of this information? If electricity deposits smoke, it might be made available in many ways. The fumes from chemical works might be condensed; and the air in large cities, otherwise polluted, might be purified and rendered innocuous. The smoke of chimneys in manufacturing works might be prevented from entering the atmosphere at all. In flour-mills and coal-mines the fine dust is dangerously explosive. In lead, copper, and arsenic works, it is both poisonous and valuable. Lead smelters labour under this difficulty of condensing the fume which escapes along with the smoke from red-lead smelting furnaces; and it was considered that an electrical process of condensation might be made serviceable for the purpose. At Bagillt, the method used for collecting or condensing the lead fume is a large flue two miles long; much is retained in this flue, but still a visible cloud of white-lead fume continually escapes from the top of the chimney. There is a difficulty in the way of depositing fumes in the flue by means of a sufficient discharge of electricity, viz. the violent draught which is liable to exist there, and which would mechanically blow away any deposited dust. But Dr. Aitken suggests that regenerators might be used along with the electricity. The warm fumes might be taken to a cold depositor, where (by the ordinary law of cold surfaces attracting warm dust-particles) the impurities would be removed, and, when purified, the air would again be taken through a hot regenerator before being sent up the chimney. By a succession of these chambers, with the assistance of electric currents, the air, impregnated with the most deleterious particles, or valuable dust, could be rendered innocuous. The sewage of our towns must be cleaned of its deleterious parts before being run into the streams which give drink to the lower animals, because an Act of Parliament enforces the process. Why, then, ought we not to have similar compulsion for making the smoke from chemical and other noxious works quite harmless before being thrown into the air which contains the oxygen necessary for the life of human beings?