repealed this session, if ever. Your steady resolutions to consume no more British goods may possibly, if persisted in, have a good effect another year. I apprehend the Parliamentary resolves and address will tend to widen the breach. Enclosed I send you Governor Pownall's speech against those resolves; his name is not to be mentioned. He appears to me a hearty friend to America, though I find he is suspected by some on account of his connexions.

TO M. DUBourg.

*

Introducing Dr. Lettsom.

London, 30 August, 1769.

THIS letter will be forwarded to you by Dr. Lettsom, a young American physician of much merit, and one of the peaceable sect of Quakers; you will therefore at least regard him as a curiosity, even though you should have embraced all the opinions of the majority of your countrymen concerning these people.

B. FRANKLIN.

ON VENTILATION.

Written by Mr. Small, the Surgeon, but containing Dr. Franklin's Observations on the Subject.

I Do not know that we have in any author particular and separate directions concerning the ventilating of hospitals, crowded rooms, or dwellinghouses; or the

* Translated from M. Dubourg's edition of Franklin's Works, Vol. II. p. 314.-EDITor.

making of proper drains for carrying off stagnant or putrid water. The want of such general information on these subjects, has induced me to endeavour to recollect all I can of the many instructive conversations I have had upon these matters with that judicious and most accurate observer of nature, Dr. Benjamin Franklin. I do this in hopes that either the Doctor himself, or some other person well qualified for the task, may follow the example set in so masterly a manner by Sir John Pringle, Baronet, when speaking on the preservation of the health of seamen.

It has long been observed, that if a number of persons are shut up in a small room, of which the internal air has little or no communication with the external, the respiration of those who are so confined renders by degrees the air of that room effete, and unfit for the support of life.

Dr. Franklin was, if I mistake not, the first who observed, that respiration communicated to the air a quality resembling the mephitic; such as the Grotto del Cane near Naples. The air impressed with this quality rises only to a certain height, beyond which it gradually loses it. The amendment begins in the upper part, and descends gradually until the whole becomes capable of sustaining life. The Doctor confirmed this by the following experiment. He breathed gently through a tube into a deep glass mug, so as to impregnate all the air in the mug with this quality. He then put a lighted bougie into the mug; and upon touching the air therein the flame was instantly extinguished; by frequently repeating this operation, the bougie gradually preserved its light longer in the mug, so as in a short time to retain it to the bottom of it; the air having totally lost the bad quality it had contracted from the breath blown into it.

At the same time that the lower part of the air is thus affected, an acrid, noxious quality may be communicated to its upper part in the room, occasioned by the volatile putrescent effluvia of the persons enclosed therein. "It is surprising," says Sir John Pringle, in his "Observations on the Diseases of the Army," fourth edition, p. 109, "in how few days the air will be corrupted in close and crowded wards; and what makes it hard to remedy the evil, is the difficulty of convincing either nurses or the sick themselves, of the necessity of opening the windows and doors at any time for a supply of fresh air."

It may be inferred from the above account of mephitic air, that such air can be but little altered by a ventilator in the ceiling of a room; and Dr. Franklin justly concluded, that in crowded rooms, and especially in bedrooms in dwellinghouses, a current of air should be kept up in the lower part of the rooms, to carry off what is thus affected. He approved of the use of chimneys for this purpose, especially when the current is quickened by a fire. Even when there is not any fire in the chimney, a current of air is constantly kept up in it, by its ascending or descending in the flue, as the weight of the internal or external air preponderates. This creates a kind of tide in the flue, conducing much to the healthiness of air in rooms; and hence we may see the injudiciousness of having chimney-boards which fit closely, and thereby prevent a salutary circulation in the air. Hence also in warm weather we may account for liquors or other things kept in a chimney being cooled, and more so if means are used to create an evaporation around them.

Every person has an atmosphere of his own, heated by the warmth of his body, which can be dissipated only by motion in the circumambient air. Thus in

warm weather, wind cools the body, by carrying off the personal atmosphere, and promoting at the same time a more free evaporation of the effluvia arising from the body. This creates a great degree of coolness on the skin. The personal atmosphere can be but little affected by a ventilator in the ceiling of a room, unless the admission of external air is so directed as to act principally on the air surrounding those in the

Dr. Franklin, when consulted on ventilating the House of Commons, represented that the personal atmosphere surrounding the members might be carried off by making outlets in the perpendicular parts of the seats, through which the air might be drawn off by ventilators, so placed, as to accomplish this without admitting any by the same channels. It will appear from what has been said, that windows placed high in the walls of churches or rooms intended for large assemblies, can contribute but little towards correcting the mephitic quality of the lower part of the air, or towards carrying off the personal atmospheres.

The experiments made for ventilating crowded rooms by that most beneficent of men, the Reverend Dr. Stephen Hales, bring evident proof how much the upper part of the air in such places is vitiated by the volatile putrescent effluvia arising from the persons present in such rooms. He at the same time showed an easy and effectual way to carry off such vitiated air. His ventilators were, however, attended with the inconveniency of occasioning smoky chimneys, by drawing off so much air, that there was not a sufficiency left to keep a current strong enough to carry the smoke up the chimney, unless a door or window was left open. The circulating ventilators in windows were intended for refreshing the air in rooms, without affecting the current of air up the chimney; but they did not affect

the mephitic air, nor the higher air near the ceiling of lofty rooms, which is most vitiated with putrescent particles; and they were besides often out of repair.

Instead of either of these, Dr. Franklin proposed that openings should be made close to the ceilings of rooms communicating with a flue, which should ascend in the wall close to the flues of the chimneys, and, where it can be done conveniently, close to the flue of the kitchen chimney; because the fire, burning pretty constantly there, would keep the sides of that flue warmer than those of the other chimneys; whereby a quicker current of air would be kept up in the ventilating flue. Such a flue might be carried from the vaults or under ground offices. This would render them drier, without altering their temperature much as to heat or cold. These ventilating flues would cause a constant discharge of the volatile putrescent effluvia without interfering with the current of air up the chimneys; while the current towards the chimney would carry off the mephitic air below. These ventilating flues would be peculiarly beneficial in bedrooms of which the ceilings are low.

Dr. Franklin mentioned an instance of a number of Germans, who on their arrival in Pennsylvania were obliged to live in a large barn; there being at that time no other place of residence fit for them. Several small windows were made on both sides of the barn under the eaves. These windows were kept constantly open, even during a severe frost in the winter; and this without any detriment to the health of the Germans. Prejudice, said he, has raised so great a dread against cold air in England, that such openings would make every person shudder at the thought of being exposed to so great a degree of cold; and therefore I did not dare to recommend a practice, the good effects of which I had known. The dormitory for the youths