FROM CADWALLADER COLDEN TO B. FRANKLIN.

Answer to the foregoing Letter respecting the Sailing of Ships across the Atlantic.

SIR,

[Date uncertair.]

There is no question but in the case you mention of a ship's being taken up in a southern latitude, and set down in one some degrees more northerly, at the same moment, she would have a degree of motion eastward; but, that it would shorten a voyage from America to Europe, I cannot think; because, as the alteration is made by insensibly small steps, it can only be so much as an alteration of the velocity in the least conceivable part of a degree of latitude is greater than the resistance of the water, which in all cases remains the same, and equally resists the smallest alteration of the velocity, as the greatest.

Suppose, for example, in the alteration of one second of latitude, how much greater will the velocity be in the southward than northward? If it be sixty miles at the equator, what will it be at one second on either side of the equator? The difference is the force which the ship can acquire from the diurnal rotation of the earth in this second. Now it may be asked, whether this difference will be sufficient to overcome the resistance of the water in any degree whatsoever; that is, whether it be not infinitely small in respect to the resistance of the body of water, which resists the motion of a ship; and if so, it can neither add to, nor diminish, the ship's way in the time she alters her latitude one second; and, if this be the case, it cannot either forward or stop her way in a greater change of latitude, because it is done by a continual addition of seconds,

or rather of less than thirds, or of any imaginable quantity; so that, according to my way of computation, in answer to your question, the difference of time in going and return will be = 0.

The shorter voyages to Europe, without doubt, are chiefly owing to the more frequent westerly winds; but this does not account for the fact, that in going to Europe a ship is generally ahead of the reckoning, or you meet with the land sooner than by the computation of the ship's way, if it be well kept; whereas, in coming to America, the reckoning is generally ahead of the ship. The true reason, I think, is from the tides. The high-water every day is nearly three quarters of an hour more easterly on the globe, than the day before; or, following the course of the moon, advancing daily about twelve degrees eastward. And therefore they every day in sailing westerly meet with the contrary current of the water sooner than they do in sailing easterly; as, in a river, in going down you meet the flood sooner than you do the ebb in going up, where the flood and ebb are nearly equal. For the difference of the force and length of the ebb more than the flood in rivers, from the force of the accumulated fresh water, cannot take place at sea.

If you think proper to give this, in your Miscellany, as the reason of the shorter voyages from America to Europe than from Europe to America, I will undertake to support it against any objection. There are some mistakes that I would be so far from being ashamed of, after I knew them to be such, that I would be vain of them, because none but those of a lively, quick, and piercing imagination can fall into them. A blockhead is incapable of making such mistakes. There is even pleasure in telling it after the mistake is discovered, and the person to whom it is told values the ingenuity

which occasioned the mistake, and, on reflection, is conscious to himself, that he would have valued himself for that very thought. There is a use likewise in mentioning these mistakes to others, to guard them against those conceptions, that please and flatter the imagination most.

Suppose the difference between the Land's End and the coast of America to be seventy-two degrees of longitude, (I choose this number to avoid fractions.) Then the same high-water on the coast of America will happen six hours later at the Land's End, and therefore a ship will meet with one tide flood against her, which would be an ebb in her favor on the coast of America; and, supposing her voyage performed in thirty days, every day equally approaching to America, she would every day have that tide lessened one thirtieth of the time, as she approaches. Some have had thoughts of calculating an equation to rectify a ship's easting and westing; but, upon reflecting that a general equation cannot serve for every ship, but must be dif ferent according to the several moulds by which ships are built, and their being loaded, or in ballast, I believe it will be of little use; for, according to the different moulds of a ship, and her being deep or light, tides have greater or less force on her way. The heavy, dull ships must make much larger allowances than the best sailers, and accordingly we generally find these heavy sailers most out of their reckoning.

I am, &c.

CADWALLADER COLDEN

in Mountains. - Petrified Shells in the Appalachian Mountains. Observations on a Tariff Law.

DEAR SIR,

Philadelphia, 16 July, 1747.

I received your favor of the 4th instant. I ought before this time to have acknowledged the receipt of the book, which came very safe, and in good order, to hand. We have many oil-mills in this province, it being a great country for flax. Linseed oil may now be bought for three shillings per gallon; sometimes for two shillings and six pence; but at New York, I have been told, it generally holds up at about eight shillings. Of this you can easily be satisfied, it being your neighbour government.

In your last, you inquired about the kind of land from which our hemp is raised. I am told it must be very rich land. Sometimes they use drained swamps and banked meadows; but the greater part of our hemp is brought from Conestago, which is a large and very rich tract of land on the banks of the Susquehanna, a large fresh-water river. It is brought down in wagons. If you should send any of your steel saws here for sale, I should not be wanting where my recommendation might be of service.

We have had as wet a summer as has been known here these thirty years, so that it was with difficulty

The Reverend Jared Eliot was a graduate of Yale College, and settled for many years as a clergyman at Killingworth in Connecticut. He had a particular fondness for philosophical studies, and published essays on agriculture, which were much read at the time, and passed through several editions. EDItor.

our people got in their harvest. In some parts of the country a great deal of hay has been lost, and some corn mildewed; but in general the harvest has been very great. The two preceding summers (particularly the last) were excessively dry. I think with you, it might be of advantage to know what the seasons are in the several parts of the country. One's curiosity in some philosophical points might also be gratified by it.

We have frequently, along this North American coast, storms from the northeast, which blow violently sometimes three or four days. Of these I have had a very singular opinion some years, viz. that, though the course of the wind is from northeast to southwest, yet the course of the storm is from southwest to northeast; that is, the air is in violent motion in Virginia before it moves in Connecticut, and in Connecticut before it moves at Cape Sable, &c. My reasons for this opinion, (if the like have not occurred to you,) I will give in my next.

I thank you for the curious facts you have communicated to me relating to springs. I think with you, that most springs arise from rains, dews, or ponds, on higher grounds; yet possibly some, that break out near the tops of high hollow mountains, may proceed from the abyss, or from water in the caverns of the earth, rarefied by its internal heat, and raised in vapor, till the cold region near the tops of such mountains condenses the vapor into water again, which comes forth in springs, and runs down on the outside of the mountains, as it ascended on the inside. There is said to be a large spring near the top of Teneriffe; and that mountain was formerly a volcano, consequently hollow within. Such springs, if such there be, may properly be called springs of distilled water.

Now I mention mountains, it occurs to tell you, that