110 Broadway, New York, Aug. 30th, 1867. Mr. LEWIS W. LEEDS was employed early in the war of the rebellion by the Sanitary Commission, as an agent to urge the necessity to the health and strength of the army, of the thorough ventilation of tents and quarters, and to devise and suggest to the proper officers the adoption of the best means for this purpose. At a later period of the war, at the suggestion of the Commission, the Quartermaster's Department engaged his services, and gave him large discretionary powers for the ventilation of hospitals. He was thus employed during all of the war, with great advantage, and the improvements which he brought about were unquestionably the means of saving thousands of lives. * * * * Mr. Leeds has a special talent for making improvements in houses of ordinary construction, by means which may be readily adopted, and with materials which may be anywhere procured without difficulty or great expense. Mr. Leeds' course of lectures on Ventilation is calculated to supply instructions of great practical utility. An invaluable addition to the health, happiness and wealth of the nation would result, if they could be delivered before every school in the country. FRED. LAW OLMSTED, First General Secretary of the Sanitary Commission. * * * * * Treasury Department, Office of the Supervising Architect, Sept. 11th, 1867. My Dear Friend. Your valuable Lectures on Ventilation have been received, and have been read with much pleasure, more especially as you are about the only person I have ever met, who, after making the ventilation and heating of buildings a specialty, has condescended to follow the laws of nature, and provide the means of adapting them to our artificial modes of life. Your lectures show a thorough study and knowledge of the principles involved, which are, like all natural principles, very simple if once understood. I have also to take this means of acknowledging the valuable aid that I have received from you on many occasions, and to express a hope that you will not despair, but relying on the adage that "truth is mighty" &c., go on with your exposures of the absurdities of the complicated and costly humbugs that are so fashionable at present, and trust you will succeed not only in your missionary labors, but find them pecuniarily profitable. Very respectfully, A. B. MULLETT, Supervising Architect. LEWIS W. LEEDS, Esq., Engineer Ventilation and Heating, Germantown, Penn'a. * * * * * FOOTNOTES.