I have now before me your Favours of Jany. 31. and March 1. the Receipt of which I ought sooner to have acknowledged.9 Your kind Congratulations on my Arrival and the Advancement of my Son, are extremely obliging.

I think I have read somewhere that Fahrenheit’s o was what he understood to be the greatest Cold of Siberia, Greenland, or any inhabited Country.1 So he graduated from thence upwards, and found the Degree of Cold in Water just freezing happened to be the 32d of his Scale. Had the Divisions of his first Scale been larger or smaller, the freezing Point would have fallen on a different Degree, and that would have been a Matter of little Importance; but it was of Use to make all his subsequent Scales alike.

I doubt with you, that Observations have not been made with sufficient Accuracy, to ascertain the Truth of the common Opinion, that the Winters in America are grown milder; and yet I cannot but think that in time they may be so. Snow lying on the Earth must contribute to cool and keep cold the Wind blowing over it. When a Country is clear’d of Woods, the Sun acts more strongly on the Face of the Earth. It warms the Earth more before Snows fall, and small Snows may often be soon melted by that Warmth. It melts great Snows sooner than they could be melted if they were shaded by the Trees. And when the Snows are gone, the Air moving over the Earth is not so much chilled; &c. But whether enough of the Country is yet cleared to produce any sensible Effect, may yet be a Question: And I think it would require a regular and steady Course of Observations on a Number of Winters in the different Parts of the Country you mention, to obtain full Satisfaction on the Point.

While I was at Cambridge in England, I assisted at an Experiment made by Dr. Hadley, then Professor of Chemistry there, at my Request, to find what Degree of Cold might be produced by Evaporation.2 The Thermometer was plung’d into a Vessel of that highly rectified Spirit the Vitriolic Ether; which as it had long stood in the Room with the Thermometer, and consequently was of the same Temperament, did not in the least alter the Height of the Mercury; but the Moment the Thermometer was taken out, and the Ether with which the Ball was wet began to evaporate from its Surface, the Mercury fell several Degrees: The Doctor repeated the Wettings, while the Evaporation was quicken’d by blowing on the Ball with a Bellows, till the Mercury fell from 65, at which it stood before the Experiment began, to 7. that is, 25 Degrees below the Freezing Point. And accordingly the Moisture condens’d, by the Coldness of the Ball, upon its Surface, froze there, and form’d by Degrees a rough Coat of Ice all round it, of near ¼ Inch thick. So it should seem, that a naked Man standing in the Wind and repeatedly wet with strong Spirit, might be frozen to Death on a Summers Day.

The Russian Philosophers3 have found that in extream Cold, Mercury itself becomes solid, and is malleable like other Metals. Hence it seems that in the State we have it, it is really a melted Metal, only it is a Metal that melts with less Heat than other Metals. Æpinus, a Member of the Academy of Sciences at Petersburg, has lately published a Latin Work in 4to. entituled, Tentamen Theoriae Electricitatis et Magnetismi; wherein he applies my Principles of Electricity to the Explanation of the various Phenomena of Magnetism, and I think with considerable Success.

The Dispute you mention, between the French and Italian Philosophers still subsists.4 You will not wonder at my supposing the latter have greatly the Advantage.

What relates to the Doctorate, I will communicate to you when I next have the Pleasure of seeing you, which I now hope soon to enjoy, as I am actually preparing to visit once more my native Country.5

You would do the Picture6 too much Honour if you had it to place where you propose. I should however send you one if I had it; but the Painter thinking the Plate ill-done, it was suppress’d. A few only came here, and none are to be had.

I have lately been favour’d with a Sight of your excellent Discourse on the Christian Union.7 As I have some ingenious Friends in Britain to whom I am sure it would be acceptable, I purpose to distribute a few among them. In the Copy you sent to Professor Williamson,8 I see you have made several manuscript Notes.9 I could wish the same Advantage to the Copies I purpose to send. May I beg the Favour of you to give it to twelve of them for which I will pay your Bookseller’s Order. With great Esteem and Respect, I am, Dear Sir, Your most obedient and most humble Servant

P.S. June 2. I send you enclos’d a little Piece [of] Æpinus’s,1 which has some relation to Points we have touch’d in our Letters. When you have perus’d it, you may forward it to Mr. Winthrop,2 who can return [it] to me when I am in Boston.