surface was not roughened by the wrinkles, or smaller waves, before-mentioned; and none or very few white caps (or waves whose tops turn over in foam) appeared in that whole space, though to windward and leeward of it there were plenty; and a wherry, that came round the point under sail, in her way to Portsmouth, seemed to turn into that tract of choice, and to use it from end to end, as a piece of turnpike-road.

It may be of use to relate the circumstances of an experiment that does not succeed, since they may give hints of amendment in future trials: it is therefore I have been thus particular. I shall only add what I apprehend may have been the reason of our disappointment.

I conceive, that the operation of oil on water is, first, to prevent the raising of new waves by the wind: and, secondly, to prevent its pushing those before raised with such force, and consequently their continuance of the same repeated height, as they would have done, if their surface were not oiled.But oil will not prevent waves being raised by another power, by a stone, for instance, falling into a still pool; for they then rise by the mechanical impulse of the stone, which the greasiness on the surrounding water cannot lessen or prevent, as it can prevent the winds catching the surface and raising it into waves. Now waves once raised, whether by the wind or any other power, have the same mechanical operation, by which they continue to rise and fall, as a pendulum will continue to swing, a long time after the force ceases to act by which the motion was first produced: that motion will, however, cease in time; but time is necessary. Therefore, though oil spread on an agitated sea may weaken the push of the wind on those waves whose surfaces are covered by it, and so, by receiving less fresh impulse, they may gradually subside; yet a considerable time, or a distance through which they

will take time to move, may be necessary to make the effect sensible on any shore in a diminution of the surf: for we know, that when wind ceases suddenly, the waves it has raised do not as suddenly subside, but settle gradually, and are not quite down till after the wind has ceased. So though we should, by oiling them, take off the effect of wind on waves already raised, it is not to be expected that those waves should be instantly levelled. The motion they have received will, for some time, continue; and if the shore is not far distant, they arrive there so soon, that their effect upon it will not be visibly diminished. Possibly, therefore, if we had begun our operations at a greater distance, the effect might have been more sensible. And perhaps we did not pour oil in sufficient quantity. Future experiments may determine this.

I was, however, greatly obliged to Captain Bentinck, for the chearful and ready aids he gave me : and I ought not to omit mentioning Mr. Banks, Dr. Solander, General Carnoc, and Dr. Blagden, who all assisted at the experiment, during that blustering unpleasant day, with a patience and activity that could only be inspired by a zeal for the improvement of knowledge, such especially as might possibly be of use to men in situations of distress.

I would wish you to communicate this to your ingenious friend, Mr. Farish, with my respects; and believe me to be, with sincere esteem,

Dear sir,

Your most obedient, humble servant,

B. FRANKLIN,

FROM DR. PERKINS, OF BOSTON, TO BENJAMIN FRANK

LIN, ESQ.

On the number of deaths in Philadelphia by Inoculation.

SIR,

Boston, Aug. 3, 1752.

This comes to you on account of Dr. Douglas : he desired me to write to you for what you know of the number that died of the Inoculation in Philadelphia, telling me he designed to write something on the small-pox shortly. We shall both be obliged to you for a word on this affair.

The chief particulars of our visitation, you have in the public prints. But the less degree of mortality than usual in the common way of infection, seems chiefly owing to the purging method designed to prevent the secondary fever: a method first begun and carried on in this town, and with success beyond expectation. We lost one in eleven one-sixth, but had we been experienced in this way, at the first coming of the distemper, probably the proportion had been but one in thirteen or fourteen.

In the year 1730 we lost one in nine, which is more favourable than ever before with us, The distemper pretty much the same then as now, but some circumstances not so kind this time.

If there be any particulars which you want to know, please to signify what they are, and I shall send them.

The number of our inhabitants decreases. On a strict inquiry, the overseers of the poor find but fourteen thousand one hundred and ninety Whites, and one thousand five hundred and forty-four Blacks, including those absent, on account of the small-pox, many of whom, it is probable, will never

return.

I pass this opportunity without any particulars of my old theme. One thing, however, I must mention, which is, that perhaps my last letters con

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tained something that seemed to militate with your doctrine of the origin, &c. But my design was only to relate the phenomena as they appeared to I have received so much light and pleasure from your writings, as to prejudice me in favour of every thing from your hand, and leave me only liberty to observe, and a power of dissenting when and if at some great probability might oblige me : any time that be the case, you will certainly hear of I am, Sir, &c.

it.

FROM BENJAMIN FRANKLIN, ESQ. OF PHILADELPHIA. In answer to the preceding.

SIR,

Philadelphia, Aug. 13, 1752.

Some

I received your favour of the 3d instant. time last winter I procured from one of our physicians an account of the number of persons inoculated during the five visitations of the small-pox we have bad in twenty-two years; which account I sent to Mr. W. V. of your town, and have no copy. If I remember right, the number exceeded eight hundred, and the deaths were but four. I suppose Mr. V. will show you the account, if he ever received it. Those four were all that our doctors allow to have died of the small-pox by inoculation, though I think there were two more of the inoculated who died of the distemper: but the eruptions appearing soon after the operation, it is supposed they had taken the infection before, in the common way.

I shall be glad to see what Dr. Douglas may write on the subject. I have a French piece printed at Paris, 1794, entitled, Observations sur la Saignee du Pied, et sur la Purgation au commencement de la Petite Verole, and Raisons de doubte contre Pinoculation.-A letter of the doctor's is mentioned in it. If he or you have it not, and desire to see it.

I will send it. Please to favour me with the particulars of your purging method, to prevent the secondary fever.

I am indebted for your preceding letter, hat business sometimes obliges one to postpone philosophical amusements. Whatever I have wrote of

that kind, are really as they are entitled, but conjectures and suppositions; which ought always to give place, place, when careful observation militates against them. I own I have too strong a penchant to the building of hypotheses; they indulge my natural indolence: I wish I had more of your patience and accuracy in making observations, on which, alone, true philosophy can be founded. And, I assure you, nothing can be more obliging to me, than your kind communication of those you make, however they may disagree with my pre-conceived

notions.

I am sorry to hear that the number of your inhabitants decreases. I some time since, wrote a small paper of thoughts on the peopling of countries, which, if I can find I will send you, to obtain your sentiments. The favourable opinion you express of my writings, may, you see, occasion you more trouble than you expected from,

Sir, yours, &c.

B. FRANKLIN.

TO BENJAMIN VAUGHAN, ESQ.

On the effects of Lead upon the human Constitution.

DEAR FRIEND,

Philadelphia, July 31, 1786. I recollect that when I had last the pleasure of seeing you at Southampton, now a twelvemonth since, we had some conversation on the bad effects of lead taken inwardly; and that at your request I promised to send you in writing a particular account of several facts I then mentioned to you, of which you