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racter of a compliment. So if I would finish
To the same. my letter in the mode, I should yet add some Salt-water rendered fresh by Distillation.thing that means nothing, and is merely civil
Method of relieving Thirst by Sea-Wl'ater. and polite. But being naturally awkward at every circumstance of ceremony, I shall not
CRAVEN-STREET, August 10, 1761. attempt it. I had rather conclude abruptly
We are to set out this week for Holland, with what pleases me more than any compli- where we may possibly spend a month, but ment can please you, that I am allowed to purpose to be at home again before the corosubscribe myself.
nation. I could not go without taking leave of you by a line at least, when I am so many letters in your debt.
In yours of May 19, which I have before To the same.
me, you speak of the ease with which salt waOn the same Subject.
ter may be made fresh by distillation, suppos
ing it to be, as I had said, that in evaporation CRAVEN-STREET, Monday, March 30, 1761. the air would take up water but not the salt SUPPOSING the fact, that the water of the that was mixed with it. It is true that diswell at Bristol is warmer after some time tilled sea water will not be salt, but there pumping, I think your manner of accounting are other disagreeable qualities that rise with for that increased warmth very ingenious and the water in distillation; which indeed seveprobable. It did not occur to me, and there- ral besides Dr. Hales have endeavoured by fore I doubted of the fact.
some means to prevent; but as yet their ma You are, I think, quite right in your opinion, thods have not been brought much into use. that the rising of the tides in rivers is not I have a singular opinion on this subject, owing to the immediate influence of the moon which I will venture to communicate to you, on the rivers. It is rather a subsequent effect though I doubt you will rank it among my of the influence of the moon on the sea, and whims. It is certain that the skin has imdoes not make its appearance in some rivers bibing as well as discharging pores ; witness till the moon has long passed by. I have not the effects of a blistering plaister, &c. I have expressed myself clearly if you have under- read that a man, hired by a physician to stand stood me to mean otherwise. You know I by way of experiment in the open air naked have mentioned it as a fact, that there are in during a moist night, weighed near three some rivers several tides all existing at the pounds heavier in the morning. I have often same time; that is, two, three, or more, high- observed myself, that however thirsty I may waters, and as many low-waters, in different have been before going into the water to parts of the same river, which cannot possibly swim, I am never long so in the water. These be all effects of the moon's immediate action imbibing pores, however, are very fine, peron that river; but they may be subsequent haps fine enough in filtering to separate salt cffects of her action on the sea.
from water; for though I have soaked (by In the enclosed paper you will find my sen- swimming, when a boy) several hours in the timents on several points relating to the air, day for several days successively in salt water, and the evaporation of water. It is Mr. Collin- I never found my blood and juices salted by son's copy, who took it from one I sent through that means, so as to make me thirsty or feel his hands to a correspondent in France some a salt taste in my mouth : and it is remarkayears since; I have, as he desired me, cor- ble, that the flesh of sea fish, though bred in rected the mistakes he made in transcribing, salt water, is not salt. Hence I imagine, that and must return it to him ; but if you think if people at sea, distressed by thirst, when it worth while, you may take a copy of it: I their fresh water is unfortunately spent, would would have saved you any trouble of that kind, make bathing-tubs of their empty water-casks, but had not time.
and, filling them with sea water, sit in them Some day in the next or the following week, an hour or two each day, they might be greatly I purpose to have the pleasure of seeing you relieved. Perhaps keeping their clothes conat Wanstead; I shall accompany your good stantly wet might have an almost equal efmamma thither, and stay till the next morning, fect; and this without danger of catching if it may be done without incommoding your cold. Men do not catch cold by wet clothes family too much.—We may then discourse on at sea. Damp, but not wet linen my possibly any points in that paper that do not seem clear give colds, but no one catches cold by bathto you; and taking a walk to lord Tilney's ing, and no clothes can be wetter than water ponds, make a few experiments there to ex- itself. Why damp clothes should then occaplain the nature of the tides more fully. In sion colds, is a curious question, the discussion the mean time believe me to be, with the of which I reserve for a future letter, or some highest esteem and regard, your sincerely future conversation. affectionate friend, B. FRANKLIN. Adieu my little philosopher. Present my
respectful compliments to the good ladies sea widen much before they arrive at it, not your aunts, and to Miss Pitt; and believe me merely by the additional waters they receive,
B. FRANKLIN. but by having their course stopped by the op
posing flood-tide; by being turned back twice To the same.
in twenty-four hours, and by finding broader
beds in the low flat countries to dilate themTendency of rivers to the Sea-Effects of the selves in ; hence the evaporation of the fresh Sun's rays on cloths of different colours.
water is proportionably increased; so that in September 20, 1761.
some rivers it may equal the springs of supply MY DEAR FRIEND,—It is, as you observed in In such cases, the salt water comes up the ri our late conversation, a very general opinion, ver, and meets the fresh in that part where if that all rivers run into the sea, or deposit there were a wall or bank of earth across, their waters there. 'Tis a kind of audacity from side to side, the river would form a lake, to call such general opinions in question, and fuller indeed at sometimes than at others, acmay subject one to censure. But we must cording to the seasons, but whose evaporahazard something in what we think the cause tion would, one time with another, be equal of truth: and if we propose our objections mo- to its supply. destly, we shall, though mistaken, deserve a When the communication between the two censure less severe, than when we are both kinds of water is open, this supposed wall of mistaken and insolent.
separation may be conceived as a moveable That some rivers run into the sea is beyond one, which is not only pushed some miles a doubt: such, for instance, are the Amazons, higher up the river by every flood tide from and I think the Oronoko and the Mississippi. the sea, and carried down again as far by The proof is, that their waters are fresh quite every tide of ebb, but which has even this o the sea, and out to some distance from the space of vibration removed nearer to the sea vand. Our question is, whether the fresh wa- in wet seasons, when the springs and brooks ters of those rivers whose beds are filled with in the upper country are augmented by the salt water to a considerable distance úp from falling rains, so as to swell the river, and farthe sea (as the Thames, the Delaware, and ther from the sea in dry seasons. the rivers that communicate with Chesapeake Within a few miles above and below this bay in Virginia) do ever arrive at the sea ? moveable line of separation, the different waAnd as I suspect they do not, I am now to ac- ters mix a little, partly by their motion to and quaint you with my reasons; or, if they are fro, and partly from the greater specific granot allowed to be reasons, my conceptions at vity of the salt water, which inclines it to run least, of this matter.
under the fresh, while the fresh water, being The common supply of rivers is from lighter, runs over the salt. springs, which draw their origin from rain
Cast your eye on the map of North Amerithat has soaked into the earth. The union of ca, and observe the bay of Chesapeake in Vira number of springs forms a river. The wa- ginia, mentioned above; you will see, commuters as they run exposed to the sun, air, and nicating with it by their mouths, the great riwind, are continually evaporating. Hence vers Susquehanna, Potowmac, Rappahan noc, in travelling one may often see where a river York, and James, besides a number of smaller runs, by a long bluish mist over it, though streams, each as big as the Thames. It has we are at such a distance as not to see the ri- been proposed by philosophical writers, that to ver itself. The quantity of this evaporation compute how much water any river discharges is greater or less, in proportion to the surface into the sea in a given time, we should meaexposed by the same quantity of water to sure its depth and swiftness at any part above those causes of evaporation. While the ri- the tide; as for the Thames, at Kingston or ver runs in a narrow confined channel in the Windsor. But can one imagine, that if all upper hilly country, only a small surface is the water of those vast rivers went to the sea, exposed; a greater as the river widens. Now it would not first have pushed the salt water if à river ends in a lake, as some do, whereby out of that narrow mouthed bay, and filled it its waters are spread so wide as that the eva- with fresh ?-The Susquehanna alone would poration is equal to the sum of all its springs, seem to be sufficient for this, if it were not for that lake will never overflow:-and if instead the loss by evaporation. And yet that bay is of ending in a lake, it was drawn into greater salt quite up to Annapolis. .ength as a river, so as to expose a surface As to our other subject, the different deequal in the whole to that lake, the evapora- grees of heat imbibed from the sun's rays by tion would be equal, and such river would end cloths of different colours, since I cannot find as a canal; when the ignorant might suppose, the notes of my experiment to send you, I as they actually do in such cases, that the must give it as well as I can from memory. river loses itself by running under ground, But first let me mention an experiment you whereas in truth it has run up into the air. may easily make yourself. Walk but a quar
Now, how many rivers that are open to the ter of an hour in your garden when the sun
shines, with a part of your dress white, and a | night, and thereby preserve the fruit from part black; then apply your hand to them al- frosts, or forward its growth ?with sundry ternately, and you will find a very great dif- other particulars of less or greater importference in their warmth. The black will be ance, that will occur from time to time to atquite hot to the touch, the white still cool. tentive minds?
B. FRANKLIN. Another. Try to fire the paper with a burning glass. If it is white, you will not easily burn it;—but if you bring the focus to
To the same. a black spot, or upon letters, written or print. On the Effect of Air on the Barometer, and the ed, the paper will immediately be on fire under the letters.
Benefits derived from the Study of Insects. Thus fullers and dyers find black cloths, of
CRAVEN-STREET, June 11, 1760. equal thickness with white ones, and hung 'Tis a very sensible question you ask, how out equally wet, dry in the sun much sooner the air can affect the barometer, when its than the white, being more readily heated by opening appears covered with wood? If inthe sun's rays. It is the same before a fire; deed it was so closely covered as to admit of the heat of which sooner penetrates black no communication of the outward air to the stockings than white ones, and so is apt soon- surface of the mercury, the change of weight er to burn a man's shins. Also beer much in the air could not possibly affect it. But sooner warms in a black mug set before the the least crevice is sufficient for the purpose; fire, than in a white one, or in a bright silver a pin-hole will do the business. And if you tankard.
could look behind the frame to which your My experiment was this. I took a number barometer is fixed, you would certainly find of little square pieces of broad cloth from a some small opening taylor's pattern-card, of various colours. There are indeed some barometers in which There were black, deep blue, lighter blue, the body of mercury at the lower end is congreen, purple, red, yellow, white, and other tained in a close leather bag, and so the air colours, or shades of colours. I laid them all cannot come into immediate contact with the out
upon the snow in a bright sun-shiney mercury; yet the same effect is produced. morning. In a few hours (I cannot now be For the leather being flexible, when the bag exact as to the time) the black being warmed is pressed by any additional weight of air it most by the sun, was sunk so low as to be be- contracts, and the mercury is forced up into low the stroke of the sun's rays; the dark the tube; when the air becomes lighter, and blue almost as low, the lighter blue not quite its pressure less, the weight of the mercury so much as the dark, the other colours less as prevails, and it descends again into the bag. they were lighter; and the quite white re Your observation on what you have lately mained on the surface of the snow, not having read concerning insects is very just and solid. entered it at all.
Superficial minds are apt to despise those What signifies philosophy that does not ap- who make that part of the creation their stuply to some use ? -- May we not learn from dy, as mere trifiers; but certainly the world hence, that black clothes are not so fit to wear has been much obliged to them. Under the in a hot sunny climate or season, as white care and management of man, the labours of ones; because in such clothes the body is the little silkworm afford employment and more heated by the sun when we walk subsistence to thousands of families, and beabroad, and are at the same time heated by come an immense article of commerce. Thc the exercise, which double heat is apt to bee, too, yields us its delicious honey, and its bring on putrid dangerous fevers? That sol. wax useful to a multitude of purposes. Andiers and seamen, who must march and labour other insect, it is said, produces the cochineal, in the sun, should in the East or West Indies from whence we have our rich scarlet dye. have an uniform of white ? That summer The usefulness of the cantharides or Spanish hats, for men or women, should be white, as flies, in medicine, is known to all, and thourepelling that heat which gives head-aches sands owe their lives to that knowledge. By to many, and to some the fatal stroke that the human industry and observation, other pro. French call the coup de soleil ? That the la- perties of other insects may possibly be here. dies' summer hats, however, should be lined after discovered, and of equal utility. A with black, as not reverberating on their faces thorough acquaintance with the nature of those rays which are reflected upwards from these little creatures may also enable manthe earth or water? That the putting a white kind to prevent the increase of such as are cap of paper or linen within the crown of a noxious, or secure us against the mischiefs black hat, as some do, will not keep out the they occasion. These things doubtless your heat, though it would if placed without. That books make mention of: I can only add a fruit-walls being blacked may receive so particular late instance which I had from a much heat from the sun in the day-time, as to Swedish gentleman of good credit. In the continue warm in some degree through the green timber, intended for ship-building at
season was over.
the king's yard in that country, a kind of stances, mixed with the air, have a similar worms were found, which every year became effect. The strong thriving state of your more numerous and more pernicious, so that mint, in putrid air, seems to show, that the the ships were greatly damaged before they air is mended by taking something from it, came into use. The king sent Linnæus, the and not by adding to it. I hope this will give great naturalist, from Stockholm, to inquire some check to the rage of destroying trees into the affair, and see if the mischief was that grow near houses, which has accompacapable of any remedy. He found, on exami- nied our late improvements in gardening, nation, that the worm was produced from a from an opinion of their being unwholesome. small egg, deposited in the little roughnesses I am certain, from long observation, that there on the surface of the wood, by a particular is nothing unhealthy in the air of woods ;
for kind of fly or beetle ; from whence the worm, we Americans have every where our counas soon as it was hatched, began to eat into try habitations in the midst of woods, and no the substance of the wood, and after some people on earth enjoy better health, or are time came out again a fly of the parent kind, more prolific. . B. FRANKLIN.
and so the species increased. The season in ?which the fly laid its eggs, Linnæus knew to
To the same, be about a fortnight (I think) in the month of May, and at no other time in the year. He on the Inflammability of the Surface of certain therefore advised, that some days before that
Rivers in America.
CRAVEN-STREET, April 10, 1774. into the water, and kept under water till the In compliance with your request, I have
Which being done by the endeavoured to recollect the circumstances of king's order, the flies missing the usual nests, the American experiments I formerly menI could not increase ; and the species was tioned to you, of raising a flame on the sur
either destroyed or went elsewhere: and the face of some waters there. wood was effectually preserved, for after the When I passed through New Jersey in 1764, first year, it became too dry and hard for their I heard it several times mentioned, that by purpose.
applying a lighted candle near the surface of There is, however, a prudent moderation some of their rivers, a sudden flame would to be used in studies of this kind. The catch and spread on the water, continuing to
knowledge of nature may be ornamental, and burn for near half a minute. But the ac3 it may be useful, but if to attain an eminence counts I received were so imperfect, that I ? in that, we neglect the knowledge and prac- could form no guess at the cause of such an
tice of essential duties, we deserve reprehen- effect, and rather doubted the truth of it. I ision. For there is no rank in natural know- had no opportunity of seeing the experiment; : ledge of equal dignity and importance with but calling to see a friend who happened to 3 that of being a good parent, a good child, a be just returning home from making it him
good husband or wife, a good neighbour or self, I learned from him the manner of it; friend, a good subject or citizen, that is, in which was to choose a shallow place, where short, a good Christian. Nicholas Gimcrack, the bottom could be reached by a walking
therefore, who neglected the care of his stick and was muddy; the mud was first to & family, to pursue butterflies, was a just object be stirred with the stick, and when a number
of ridicule, and we must give him up as fair of small bubbles began to arise from it, the ! game to the satyrist.
candle was applied. The flame was so sudB. FRANKLIN. den and so strong, that it catched his ruffle
and spoiled it, as I saw. New Jersey having
many pine-trees in many parts of it, I then To Dr. Joseph Priestley. imagined that something like a volatile oil of
turpentine might be mixed with the waters Effect of Vegetation on Noxious Air.
from a pine-swamp, but this supposition did That the vegetable creation should not quite satisfy me. . I mentioned the fact to restore the air which is spoiled by the animal some philosophical friends on my return to part of it, looks like a rational system, and England, but it was not much attended to. seems to be of a piece with the rest. Thus I suppose I was thought a little too credulous. fire purifies water all the world over. It In 1765, the Reverend Dr. Chandler repurifies it by distillation, when it raises it in ceived a letter from Dr. Finley, President of vapours, and lets it fall in rain; and farther the College in that province, relating the same still by filtration, when, keeping it fluid, it experiment. It was read at the Royal Soci. suffers that rain to percolate the earth. We ety, November 21, of that year, but not knew before, that putrid animal substances printed in the Transactions; perhaps because were converted into sweet vegetables, when it was thought too strange to be true, and mixed with the earth, and applied as manure; some ridicule might be apprehended, if any and now, it seems, that the same putrid sub-member should attempt to repeat it, in order VOL. II....2 Z
to ascertain, or refute it. The following is a portionable. I will however endeavour to copy of that account.
explain to you what occurred to me, when I “A worthy gentleman, who lives at a few first heard of the fact. miles distance, informed me, that in a certain I suppose it will be generally allowed, on small cove of a mill-pond, near his house, he a little consideration of the subject, that was surprised to see the surface of the water scarce any drop of water was, when it began blaze like inflamed spirits. I soon after went to fall from the clouds, of a magnitude equal to the place, and made the experiment with to that it has acquired, when it arrives at the the same success. The bottom of the creek earth; the same of the several pieces of hail; was muddy, and when stirred up, so as to because they are often so large and so weighty, cause a considerable curl on the surface, and that we cannot conceive a possibility of their a lighted candle held within two or three being suspended in the air, and remaining at inches of it, the whole surface was in a blaze, rest, there for any time, how small soever; as instantly as the vapour of warm inflamma- nor do we conceive any means of forming ble spirits, and continued when strongly agi- them so large, before they set out to fall. It tated, for the space of several seconds. It was seems then, that each beginning drop, and at first imagined to be peculiar to that place; particle of hail, receives continual addition in but upon trial it was soon found, that such a its progress downwards. This may be sevebottom in other places exhibited the same phe- ral ways: by the union of numbers in their
The discovery was accidentally course, so that what was at first only descendmade by one belonging to the mill.” ing mist, becomes a shower; or by each par
I have tried the experiment twice here in ticle, in its descent through air that contains England, but without success. The first was a great quantity of dissolved water, striking in a slow running water with a muddy bot- against, attaching to itself, and carrying down tom. The second in a stagnant water at the with it such particles of that dissolved water, bottom of a deep ditch. Being some time as happen to be in its way; or attracting to employed in stirring this water, I ascribed an itself such as do not lie directly in its course intermitting fever, which seized me a few by its different state, with regard either to days after, to my breathing too much of that common or electric fire; or by all these causes foul air, which I stirred up from the bottom, united. and which I could not avoid while I stooped, In the first case, by the uniting of numbers, endeavouring to kindle it. The discoveries larger drops might be made, but the quantity you have lately made, of the manner in which falling in the same place would be the same inflammable air is in some cases produced, at all heights; unless, as you mention, the may throw light on this experiment, and ex- whole should be contracted in falling, the plain its succeeding in some cases, and not lines described by all the drops converging, in others. With the highest esteem and re- so that what set out to fall from a cloud of many spect,
B. FRANKLIN. thousand acres, should reach the earth in per
haps a third of that extent, of which I some
what doubt. In the other cases we have two To Dr. Percival.
1. A dry glass bottle filled with very cold On the different quantities of Rain which fall water, in a warm day, will presently collect
at different heights over the same ground.- from the seemingly dry air that surrounds it Read in the Philosophical Society of Manchester, January 21, 1784.
a quantity of water, that shall cover its sur
face and run down its sides, which perhaps is On my return to London I found your fa- done by the power wherewith the cold water vour of the 16th of May (1771.) I wish I attracts the Auid, common fire that had been could, as you desire, give you a better expla- united with the dissolved water in the air, and nation of the phenomenon in question, since drawing the fire through the glass into itself, you seem not quite satisfied with your own; leaves the water on the outside. but I think we want more and a greater va 2. An electrified body left in a room for riety of experiments in different circumstances, some time, will be more covered with dust to enable us to form a thoroughly satisfactory than other bodies in the same room not elechypothesis. Not that I make the least doubt trified, which dust seems to be attracted from of the facts already relate as I know both the circumambient air. lord Charles Cavendish and Dr. Heberden to Now we know that the rain, even in our be very accurate experimenters: but I wish hottest days, comes from a very cold region. to know the event of the trials proposed in Its falling sometimes in the form of ice, shows your six queries; and also, whether in the this clearly; and perhaps even the rain is same place where the lower vessel receives snow or ice, when it first moves downwards, nearly twice the quantity of water that is re- though thawed in falling: and we know that ceived by the upper, a third vessel placed at the drops of rain are often electrified: but those half the height will receive a quantity pro- causes of addition to each drop of water or