magnified, certainly there are great multitudes of people from Pennsylvania, Jersey, New York, etc., gone and going to Kentucky. Either Mr. Rittenhouse or another gentleman who came from thence (I forget which) said he met thousands of people going there, and I heard the same repeatedly while at Philadelphia and on the road. If you desire any particular inquiries, I can make them for you, and will when you send me a detail of them. I am, dear sir, Your friend and brother, JEREMY BELKNAP. Do n't forget the scale for the thermometer. [To Rev. Mr. Belknap.] IPSWICH, March 3, 1786. Dear Sir-When I first cast my eye over the scale of your thermometer, I imagined you might apply a scale similar to Fahrenheits, but, on further examination, suspect whether you will be able to do it, except by placing Fahrenheit's thermometer by the side of yours. The necessary data on your scale will be two fixed points, that of freezing, and either that at which spirits or water boil. Neither of these seem to be noted on your scale with sufficient precision. I find on your scale 55° cold, 55° frost, and 77° hard frost. Is 65° the precise point of freezing? If it be, you have one of the necessary fixed points given. But, then, you want another, viz., that of boiling spirits or water which are not expressed, for from 7° above 0 to 5° is the region of extreme heat, and then 15° sultry, leaving it altogether uncertain at what point spirit and water boil. There may be difficulty in determining the point at which water boils in a spirit thermometer, but there can be none in ascertaining the point at which spirits boil. On Fahrenheit's scale, freezing point is at 32°. Spirits boil at 175°, and water at 212. These are the points from which the scale is graduated. Now, if you can find the point of freezing, and that at which spirits boil on your scale, you can easily construct and apply one similar to Fahrenheit's, by extending the line from off the scale of your thermometer at freezing point on to your new scale, and do the same from the point at which spirits boil, then divide the space between these points into 143 equal parts, viz., the number of degrees between 32 and 175, and by continuing your equal divisions, you may go as far above and below those points as you please. If you can satisfy yourself with respect to the freezing point, I should suppose you may ascertain that at which spirits boil by immersing your thermometer in spirits, and producing heat sufficient to make them boil. Care ought to be taken that all parts of the spirits in your tube be equally heated by immersing the tube nearly as far in the spirits as the spirits within the tube will rise when the spirits without begins to boil. Your spirits ought to be well rectified, for the more water they contain the more heat will be required to make them boil, and consequently the error will be so much the greater. You may rectify your spirits (New England rum will answer) by dissolving four ounces of alkaline salts (pearl-ash is commonly used) in one quart, and so in proportion, if the quantity be greater or less. A thought has this instant come into my mind, which I wonder should not have occurred before. I see no difficulty that can attend your immersing your thermometer in water and then applying heat sufficient to cause the spirits to boil in the tube. Carefully note the point on your scale, increase the heat until your water boils, which will give you the point corresponding to 212° on Fahrenheit's scale. Water, I am sensible, can not acquire a heat above 212°, or that of boiling, but I presume spirit confined in a tube, purified from air, is capable of receiving a much greater heat than that of water, as there is no possibility of evaporation. But this is a branch of natural philosophy to which I have never very much attended, and of which you have the best knowledge. Fahrenheit's scale is frequently adjusted by Reaumur's thermometer, and vice versa, which is easily done, because the fixed points are given on both of them. By the way, Reaumur's scale, on which freezing point, the only point which seems to be properly fixed in nature, is 0, and the number of degrees ascend and descend, appears to me much more natural than any that has been invented. But I think, however, it has its faults. The principal one is, the largeness of the divisions. If I remember right, water boils at 100°, which makes the dis tance of the degrees much too great for nice experiments. In one of the late volumes of the Transactions of the R. S. there is a new improvement on thermometers. A thermometer on a new construction has been invented by Mr. Wedgewood for the purpose of ascertaining the degree of heat in which all the different species of metals will fuse, and the scale so graduated as to be connected with that of Fahrenheit's. I would send you the principles and methods of construction as a curiosity, but I have not the volume at this time by me. It is much to be regretted that thermometer and barometer tubes are not made in this country, and in this part of it. I am persuaded glass-works, were they undertaken by some person or persons of property, and under the direction of a workman who was well acquainted with the business, might be made very profitable to the proprietors, and of general utility. It is an employment that requires few hands, we have the materials in plenty, and the consumption of the various kinds of glassware is very great. At such works we might be furnished with a great variety of glass philosophical instruments, for which we are now obliged to send to Europe, or go without them. Might not this business be carried on to advantage at Dover or Portsmouth? I thank you for your kind exertions to procure me a botanical correspondent at the southward. I have thought of requesting the favor of Mr. Hazard of applying to the Captain of the next ship that shall sail for the East Indies, and desire him to procure the seeds of certain vegetable productions, natives of that country. The varnish tree will, without the least doubt, flourish here; and I am much inclined to believe one if not two species of tea will grow with us. Probably in the Ohio Country it might be propagated to great advantage. Not having any personal acquaintance with Mr. Hazard, I feel some reluctance to make the request. I am, dear sir, Most sincerely yours, M. CUTLER. [To Rev. Dr. Belknap.] IPSWICH, April 1, 1786. My Dear Friend:We have so many facts and circumstances related of swallows being found in the mud in the winter, or seen to come out of it in the spring, that there seems to be no ground to doubt whether they are birds of passage or not. The most incontestible proof of their retreat into the mud in the fall is a fact related by Mr. Dexter,* in a paper printed in our Memoirs, which you will soon see, and another I have received from Prof. Williams, who assures me that a few winters ago he had several swallows brought (to him, which he carefully examined) by a person who said he found them in the mud on the side of a pond not far from Cambridge. The toads you mention on the scaffold is a curious matter, but the common opinion of their falling from the clouds in rain can not, I believe, be very easily supported on philosophical principles. Might not the small toads found on the scaffold be of the species called tree toads, which you know will ascend trees? And may not those toads and frogs we commonly see hopping about after a shower be invited abroad from the places of their retreat in dry weather by the cool, moist state of the air, and the descent of rain, or in search of food? The Memoirs of the Academy are now ready to be delivered to subscribers, but I have not yet received any of them from the printers. As soon as they come to hand, I will forward a volume to you. Mrs. Cutler joins me in kind respects to you and Mrs. Belknap. I am your most affectionate friend and brother, M. CUTLER. * IIon. Samuel Dexter, LL.D., in a paper published in the Memoirs of the American Academy of Arts and Sciences, volume 1, relates, upon the authority of Judge Foster, of Brookfield, that when a certain pond was drained in that season of the year when swallows first appear, a multitude of swallows disengaged themselves from the mud in the bottom; and gives other reasons for his belief that the mud is their winter resting-place. [To Rev. Dr. Belknap.] IPSWICH, July 25, 1786. Dear Sir:Mr. Samuel Vaughan, Jr., of Philadelphia, called on me lately, to inform me of his determination to visit the White Mountains, and to consult about the matter. The season being too far advanced for a visit this summer, Mr. Vaughan proposes to send to Europe in the fall for every kind of instrument we may want, which will arrive in the spring. About midsummer, a tour is proposed, but I wish to consult you, and hope for the pleasure of your company. I saw Colonel Waters the day after commencement, and desired him to put himself in readiness. He appeared much pleased, and proposes to provide well in comfortables for the journey. Mr. Vaughan has been at the Eastward for several weeks. He returned last week to Boston, and proposed another tour cast in about a fortnight, but he informed me yesterday by letter that he was going on to Philadelphia. He is, however, to return soon, and will be at Pownalboro' on the 28th of August, when a quantity of land belonging to his father is to be sold at that place. In this journey, he intends to call on you. He has made the tour of Europe, and appears to be acquainted with many distinguished literary characters in the countries through which he traveled. Mineralogy has been his favorite study. He has furnished himself with the best apparatus ever imported into America, and, I presume, is well acquainted with the subject. He seems to have a truly philosophic mind, and appears sensible, curious, and very agreeable. He writes me that Count Castiglioni is now at Philadelphia, and has been much delighted with his tour to the Southern States. He went as far as Savannah, and returned behind the Blue Mountains. He stays till the beginning of August in Philadelphia, when he proceeds to New York and Rhode Island, and embarks for Europe in November. Mr. Guild, in his late tour to the Southward, procured me a pamphlet entitled Arbustrum Americanum, by Humphrey Marshall, of Chester County, in Pennsylvania. It is a description of the native forest trees and shrubs of the American United States, alphabetically arranged. He has given the |