CHAPTER. III. Of the cause of the ascent of smoke. Illustration of the subject by familiar comparisons and experiments. Of chimnies which affect and cause each other to smoke. Of chimnies which smoke from want of air. Of the eddies of wind which sometimes blow down chimnies, and cause them to smoke. Explanation of the figures. ESSAY IV. ADVERTISEMENT The Author thinks it his duty to explain the reasons which have induced him to change the order in which the publication of his Essays has been announced to the Public.--Being suddenly called upon to send to Edinburgh a person acquainted with the method of altering Chimney Fire-places, which has lately been carried into execution in a number of houses in London, in order to introduce these improvements in Scotland, he did not think it prudent to send any person on so important an errand without more ample instruction than could well be given verbally; and being obliged to write on the subject, he thought it best to investigate the matter thoroughly, and to publish such particular directions respecting the improvements in question as may be sufficient to enable all those, who may be desirous of adopting them, to make, or direct the necessary alterations in their Fire-places without any further assistance. The following Letter, which the Author received from Sir John Sinclair, Baronet, Member of Parliament, and President of the Board of Agriculture, will explain this matter more fully: You will hear with pleasure that your mode of altering Chimnies, so as to prevent their smoking, to save fuel, and to augment heat, has answered not only with me, but with many of my friends who have tried it; and that the Lord Provest and Magistrates of Edinburgh have voted a sum of money to defray the expences of a bricklayer, who is to be sent there for the purpose of establishing the same plan in that city. I hope that you will have the goodness to expedite your paper upon the management of Heat, that the knowledge of so useful an art may be as rapidly and as extensively diffused as possible.--With my best wishes for your success in the various important pursuits in which you are now engaged, believe me, with great truth and regard, Your faithful and obedient servant John Sinclair Whitehall, London, 9th February 1796. CHAPTER. I. Fire-places for burning coals, or wood, in an open chimney, are capable of great improvement. Smoking chimnies may in all cases be completely cured. The immoderate size of the throats of chimnies the principal cause of all their imperfections. Philosophical investigation of the subject. Remedies proposed for all the defects that have been discovered in chimnies and their open fire-places. These remedies applicable to chimnies destined for burning wood, or turf, as well as those constructed for burning coals.