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the transit instrument, which was forty guineas, and then shall apply for the whole to Mr. Mauduit. By the way, I wonder that I have not heard from you of the receipt of that instrument, which went from hence in September by Captain Watt. I hope it got safe to hand and gave satisfaction. The ship was the same that Mr. Rogers went in, who I hear is arrived ; and by him too I sent the Philosophical Transactions, with a number of copies of your paper as printed separately. But I have no letter from you since that by the young gentleman you recommended to me, grandson to Sir William Pepperell, which I think was dated about the beginning of October, when you could not have received them.

By a late ship, I sent your College a copy of the new edition of my Philosophical Papers; and others, I think, for yourself and for Mr. Bowdoin. I should apologize to you for inserting therein some part of our correspondence without first obtaining your permission; but, as Mr. Bowdoin had favored me with his consent for what related to him, I ventured to rely upon your good-nature, as to what related to you, and I hope you will forgive me.

I have got from Mr. Ellicot the glasses, &c. of the long Galilean telescope, which he presents to your college. I put them into the hands of Mr. Nairne, the optician, to examine and put them in order. I thought to have sent them by this ship, but am disappointed. They shall go by the next, if possible.

There is nothing new here in the philosophical way
at present.
With great and sincere esteem, I am, Dear Sir,
Your most obedient and humble servant,

B. FRANKLIN.

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P. S. There is no prospect of getting the duty acts

repealed this session, if ever.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.

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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.

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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 room. 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

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