hand sheet is turned down to the right. Four sheets are now laid down, with the seam or joint rising to the ridge; and thus the work is continued, both vertically and horizontally, till the roof be covered, the sides and ends of each sheet being alternately, each way, undermost and uppermost.

The price for copper, nails, and workmanship, runs at about eight pounds ten shillings per hundred weight, or two shillings and three pence per foot, superficial, exclusive of the lappings; and about two shillings and eight pence per foot upon the whole; which is rather above half as much more as the price of doing it well with lead.

TO THOMAS PERCIVAL.*

On the different Quantities of Rain which fell at different Heights over the same Ground.

On my return to London I found your favor of the 16th of May (1771). I wish I could, as you desire, give you a better explanation of the phenomenon in question, since you seem not quite satisfied with your own; but I think we want more and a greater variety of experiments in different circumstances, to enable us to form a thoroughly satisfactory hypothesis. Not that I make the least doubt of the facts already related, as I know both Lord Charles Cavendish and Dr. Heberden

This letter is without date, but was probably written in the year 1771, since it was in answer to a letter dated in May of that year. It was first printed in the Memoirs of the Literary and Philosophical Society of Manchester, Vol. II. p. 110, having been communicated to the Society by Dr. Percival, and read on the 21st of January, 1784.- EDItor.

1

to be very accurate experimenters; but I wish to know the event of the trials proposed in your six queries; and also, whether in the same place where the lower vessel receives nearly twice the quantity of water that is received by the upper, a third vessel placed at half the height will receive a quantity proportionable. I will however endeavour to explain to you what occurred to me, when I first heard of the fact.

I suppose it will be generally allowed, on a little consideration of the subject, that scarce any drop of water was, when it began to fall from the clouds, of a mag-, nitude equal to that it has acquired, when it arrives at the earth; the same of the several pieces of hail; because they are often so large and so weighty, that we cannot conceive a possibility of their being suspended in the air, and remaining at rest there, for any time, how small soever; nor do we conceive any means of forming them so large, before they set out to fall. It seems then, that each beginning drop, and particle of hail, receives continual addition in its progress downwards. This may be several ways; by the union of numbers in their course, so that what was at first only descending mist, becomes a shower; or by each particle, i. descent through air that contains a great quantity of dissolved water, striking against, attaching to itself, and carrying down with it such particles of that dissolved water, as happen to be in its way; or attracting to itself such as do not lie directly in its course by its different state with regard either to common or electric fire; or by all these causes united.

In the first case, by the uniting of numbers, larger drops might be made, but the quantity falling in the same place would be the same at all heights; unless, as you mention, the whole should be contracted in falling, the lines described by all the drops converging,

so that what set out to fall from a cloud of many thousand acres, should reach the earth in perhaps a third of that extent, of which I somewhat doubt. In the other cases we have two experiments.

1. A dry glass bottle filled with very cold water, in a warm day, will presently collect from the seemingly dry air that surrounds it a quantity of water, that shall cover its surface and run down its sides; which perhaps is done by the power wherewith the cold water attracts the fluid common fire that had been united with the dissolved water in the air, and drawing the fire through the glass into itself, leaves the water on the outside.

2. An electrified body, left in a room for some time, will be more covered with dust than other bodies in the same room not electrified, which dust seems to be attracted from the circumambient air.

Its falling sometimes clearly; and perhaps when it first moves

Now we know that the rain, even in our hottest days, comes from a very cold region. in the form of ice shows this even the rain is snow or ice, downwards, though thawed in falling; and we know that the drops of rain are often electrified. But those causes of addition to each drop of water, or piece of hail, one would think could not long continue to produce the same effect; since the air, through which the drops fall, must soon be stripped of its previously dissolved water, so as to be no longer capable of augmenting them. Indeed very heavy showers, of either, are never of long continuance; but moderate rains often continue so long as to puzzle this hypothesis; so that upon the whole I think, as I intimated before, that we are yet hardly ripe for making one.

B. FRANKLIN,

FROM W. SMALL TO B. FRANKLIN.

Opinions of the Ancient Physicians respecting Catarrhs,

or Colds.

DEAR SIR,

Birmingham, 10 August, 1771.

The reason of your having no sooner received the quotation from Celsus, is, that I wished to employ my very first leisure in looking into several other ancient books for passages to the same purpose, and to send you all together. But Mr. Keir having told me of your desire to see that immediately, you have it almost alone.

In the article "De Tabe" in his third book, treating of the cure, he says, "Cavendæ distillationes, ne, si quid cura levarit, exasperent; et ob id, vitanda cruditas, simulque et sol et frigus."* Here indigestion seems to be reckoned the principal cause. If you have not attended to that particular before, you may be surprised to find sunshine among the causes of colds, but such is the doctrine of all the ancients. A passage about the instruments of cure in coughs may perhaps amuse you, "Utilis etiam in omni tussi est peregrinatio, navigatio longa, loca maritima, natationes." +

From several things in Xenophon and in Plato, the prevailing opinion in their time seems to have been, that what we now commonly call colds and catarrhs, arose almost solely from excess and indolence. On this account Xenophon says, that in Persia in the days of Cyrus, to spit or to blow a nose was infamous

"Great caution should be observed, when relief is once obtained, lest catarrhs are made worse; indigestion also, as well as exposure to the sun and cold air, ought to be avoided."

"In all coughs it is found beneficial to take long journeys and voyages, to reside on the sea-coast, and to use sea-baths."

Plato often commends simple spare diet, but in one place he says it prevents all catarrhs. Whether he means precisely what we call catarrhs, however, in that passage, may be doubted.

I do not recollect any absolutely express testimony in your favor from Hippocrates. Mucus (of the nose) and saliva he judges to be signs of repletion; and he maintains that persons who drink and eat sparingly are free from diseases occasioned by moisture. Abundance may be found in Galen to your purpose. A modern author, who ought to have understood this subject, for he has written so great a book about catarrhs,* that you had better have twenty colds than read it, is of your opinion. "Illa, illa, inquam, cibi potusque abundantia citat catarrhos. Eosdem abigunt frugalitas et labor. Ut ex luxu et otio nascuntur catarrhi, ita horum medicina est in sobrietate, in continentiâ, in exercitationibus corporis, in mentis tranquillitate. Quotusquisque vero hæc precepta, has leges vivendi custodit? Homo frugi est rara avis, &c. Hinc nemo mortalium fere est sine catarrhis."†

Mr. Boulton will soon present you with one of the boxes with invisible hinges. He has astonished our rural philosophers exceedingly by calming the waves à la Franklin. ↑

I am trying some experiments in relation to the

This book upon the Catarrh is probably that of Schneiderus, consisting of four volumes, 4to.

"Eating and drinking too much is sufficient of itself, I say, to produce catarrhs. Temperance and active pursuits on the contrary drive them away. As catarrhs are produced by luxury and indolence, so the remedy for these is to observe sobriety, continence, exercise of body and tranquillity of mind. How few observe these precepts! Temperance indeed is very rare. Hence very few escape catarrhs."

That is, by means of oil, according to the experiments mentioned in this volume under the date of January 27th, 1773, p. 355.-EDIitor.