I was honoured with your letter of the 29th. of December only last night, and take the first moment of answering it, presuming to offer a few remarks on the objects you have in view, by way of preface.

It appears that many mistakes respecting the animal and vegetable productions of America have arisen from the precipitancy of European philosophers in deciding upon slight evidence; as well as from the propensity of mankind to extend partial into general conclusions. Your notes respecting Virginia furnish ample proofs of this.

Those Europeans however who have disparaged the New World have not only been imperfectly acquainted with their subject; but seem to have overlooked the original destitute state of Europe which is said to have borrowed many of its valuable animals and vegetables from other countries. We hear of a Ceres, a Bacchus, and a Minerva deified for the introduction of corn, of wine, and of oil into our quarter of the globe; and we can very easily credit these traditions from the accounts given of the gradual spread of the two latter productions in the Southern parts of Europe. We are not able (it is said) in this island of Great Britain to boast of a single fruit as indigenous among the number that now appear at our tables, and it is clear from authentic accounts, that we have as little claim to the original of most of our esculent vegetables, which are now so common. I must add that the species both of our fruits and common esculent vegetables are still very few in number, though we have taken some pains to traverse the globe to collect or add to them, and have likewise called in experienced art to our assistance. It is observable also that several of our present English fruits have had their reputed origin from the neighbourhood of the Black Sea, whose climate bears a very particular resemblance to those parts of Eastern North America which lie in correspondent latitudes. I may add that from various authentic relations, Eastern North America appears to exhibit (notwithstanding the opinions that have been entertained respecting it) a fair Model in general of the climate of all the inland and Eastern quarters of our Northern Hemisphere.

I have sometimes thought that if Eastern North America had been peopled by old and civilized nations, some ages before the birth of Christ, and had at that time accumulated in it (wherever the climates were analagous) not only the productions (vegetable and animal) of the Western and Southern parts of its double continent, but those from China and Japan, in addition to all those productions which accident, as well as diligence and art might have enabled it to discover and propagate within itself: I have thought that if a people, so circumstanced in those parts, had at that period discovered Western Europe, similar remarks would probably have occurred (after a time) among their speculative philosophers, on the rude and ill provided condition of the New World (as our part of it would then have been called). A civilized Chinese, given to speculation and theory, might in similar terms now speak of Western North America; though Western North America, there is good reason to think, is the exact counterpart, as to climate, of Europe and part of Africa. Indeed it is to be hoped that in future ages it will become alike civilized and alike abounding in the good things of this life with Western Europe, and when that period arrives, the voyages of Cook will be read with the same degree of curiosity by Western Americans with which Western Europeans now peruse the accounts of Germany, Gaul and England given by Tacitus and Cæsar. Certain it is, that Europeans in general do not at present think worse of America than some of the Greeks and Romans formerly thought of those parts of Europe, which now make the most brilliant figure of any countries upon the globe.

I do not mean to suggest by any of these remarks, that there are not certain considerable and characteristic distinctions between the climate of this quarter of the world and that of your own. But every circumstance of this sort, were it to be entered into, would come under a separate head of discussion. All that I mean to affirm is, that there is nothing peculiar and ill-fated in your own climate and soil, compared with that of the globe at large; and that nature, after she has had proper time to make a full display of herself, will be found as provident to you, as to the Northern Hemisphere in general. Indeed it has never appeared her intention to accumulate all her favours upon any one situation: her gifts are dispersed; and men are to be made acquainted and united among each other, by their attempts to assemble and exchange them.

I am truly happy to see that in your work, you have with so much success combated the opinions of certain European philosophers on some of these subjects respecting Eastern America. I think the Recherches sur Les Americains contain nearly three volumes of errors, believed in Europe because boldly asserted, and till lately never controverted. Monsr. De Buffon and the abbé Raynal in particular among the French, and Dr. Robertson and others with us, have largely imbibed these errors; but the time has arrived when science, industry and art on your side of the water, will soon furnish materials to overthrow the whole of them, and even to efface their memory.

As to the supposed humidity of the atmosphere of Eastern North America, compared with that of Europe, (your desire of enquiring into which gave occasion to the letter you have done me the honour to write) European philosophers seem to have formed their conclusion respecting this subject principally from three sources. First, from the excessive vehemence of the rains which fall at times in the colonized parts of Eastern America, especially to the Southward. Next from the cultivated parts of the West Indies (a supposed appendage of the part of America in question) being divided into small islands exposed to the sea air. And lastly from the inhabitants of all our colonies having generally chosen for the seat of their plantations and settlements the banks of the sea or of rivers; or else low lands, swamps and mill ponds; either for the sake of cheap carriage and easy cultivation, or of the advantages for machinery afforded by such situations; preferring the speedy acquisition of wealth, to health and happiness, and the other slower, though more permanent and substantial modes of attaining riches. I do not defend the necessity of the last of these causes; I think it an opprobrium to my American friends, and that it much more deserves legislative attention in each particular state, than matters of trade, or other matters of a more delicate nature which legislators seldom treat with any success. But after allowing for all these causes in their fullest extent, I cannot but incline to the opinion which yourself and Dr. Franklin have assumed on the subject alluded to, as far as respects the Eastern and probably the internal parts of North America.

Trusting to your kind forgiveness of a few observations made in favour of a country from which I am in part descended, I shall now have the pleasure of attending more immediately to the particulars respecting which you did me the honour to apply to me.

I have been some time acquainted with Dr. Franklins observations on Hygrometers, since published in the second volume of the Philadelphian Philosophical Transactions. He showed me the manuscript when in an unfinished state, in which it had long lain by neglected, and which occasioned me to express considerable regret, and I had the pleasure to find that the paper was soon after completed and forwarded to Mr. Nairne. I think it in his usual manner, novel, sagacious, and simple; and it appears the more useful, as extreme diversity of opinion, if not difficulty has long prevailed respecting hygrometers constructed upon other principles.

Mr. Nairne made an instrument pursuant to Dr. Franklins hint, of which he some time ago favoured me with a drawing and description, a copy of which I have annexed. My objection to the plan of this instrument, though otherwise ingenious, is, that the motion of the pin produces greater changes in the position of the smaller arm and consequently of the index, when the smaller arm is at right angles to the line of motion of the pin, than when oblique.* The remedy of this difficulty must either lie in certain complex machinery annexed to the arm, or in a complex division of the scale to which the index points: but as the result sought after, is made to depend upon the comparison of two instruments, the less complex the plan is, the better.

I have therefore been led to employ Dr. Franklin’s principles in a manner more simple. As the case of the shutter of the magnetbox seemed to prove that a small plate of wood, cut thin, might exhibit considerable variations of dimension across the grain, I at first directed a number of such plates to be cut square, two of the sides of which should run parallel to the grain or fibre of the wood; and the other two to be at right angles; designing to make the invariable serve as measures to the variable sides. But as a small scale might leave room for doubts, and if the squares were much enlarged, other inconveniences might arise, I directed a thin and narrow stripe, or fillet of wood, to be cut across the grain of the widest plank of Mahogony that could be found; and that from the same wood a staff should be cut, in which the fibres should run longitudinally; the staff being both solid and long enough to allow of a groove in it for the purpose of receiving the fillet. (The fillet having the cross grain, would thus lie freely in the groove of the staff which is oppositely grained, nearly as a pocket comb lies in its tortoise shell case.) The staff being made a little longer than the fillet, when the two were brought to coincide at one of their extremities, it would be easy to mark upon the staff the standard point, to which the other end of the fillet reached in the standard country; and afterwards, to mark the point to which the fillet should stretch or shrink in other countries, accordingly as they were moister or drier.

An instrument of this kind, which, by being composed of two parts, carries along with it its own standard and allows its changes to be reduced into well known and ordinary measures, I had the pleasure about a fortnight ago to send to Mr. White, who is appointed principal surgeon to attend the proposed expedition with our convicts to Botany Bay in the South Seas. It is one of its advantages, that any carpenter can easily construct the like out of any kind of wood.

I was sorry not to have been able to inspect the instrument sent to Mr. White. But Messrs. Nairne & Blunt, who made it, having undertaken to make a second for me, I have the honour to request your acceptance of it, Coll. Smith offering the means of conveying it to you.

I have had no trial of this little contrivance, but I foresee several precautions necessary to be observed. The first is, that of placing the instrument in corresponding situations in the countries of trial; since considerable differences may arise from the neighbourhood of the sea and other waters, or from swampy or mountainous situations; and other differences again from the apartments in which the instruments are preserved, either as to their being with or without fires, their aspect, elevation from the ground, and other circumstances. A second precaution is, that of noting the state of the weather, or the season at the period of observation; for it is well known, for instance, that the doors and windows of houses will shut more or less closely, according to the state of the air as to humidity, at different periods in the same country. A third precaution is, that of using for the construction of the instrument none but seasoned wood. It is partly owing to a neglect of this that the floor of the room where I now write, has large openings between each of its boards; though neither the boards, nor the rafters that run across the boards, appear to have altered in their dimensions longitudinally; and in like manner that the door of a deal box (in which, when lined with baize, fire arms may long be kept dry and free from rust) and which is fastened to the wainscot of my bedroom, has shrunk considerably cross ways, though two wooden bars, that stretch across this door at right angles, appear to retain their original dimensions: (These effects being also partly owing to the removal of the wood from an open timber yard, or carpenters shed, into a warm inhabited house). The warping of the parts of the instrument may call for a fourth precaution; and to remedy this defect, when it takes place in the filleting, the filleting may be measured when laid under the pressure of a moderate weight; while the shape of the staff may be best preserved by giving it such a degree of solidity as shall produce compensations to the action of any one part of its substance against any other part of it. The filleting may be two inches wide and 1/10 inch thick, as recommended by Dr. Franklin, and a section across the staff may form a square of 2. or 3 inches.

Should the supposition, that certain woods do not vary in their longitudinal dimensions prove untrue, it will not affect the credit to be given to the instrument in question, provided the variation is different in its degree from that occurring crosswise.

I am pleased with the ingenuity of Mr. Rittenhouse’s idea, which was perfectly new to me; but I fear the variations of no two hygrometers, on his plan of construction can be depended upon as at all corresponding, which is certainly one objection to it; and I think a second objection to it is, that the degrees of variation in the same instrument, must be far from being equable in their measurement, compared with the degrees of change taking place in the atmosphere.

I have ordered a box of magnets from Messrs. Nairne & Blunt, similar to that which was in the possession of Dr. Franklin, which will accompany the hygrometer, its case being formed out of the same piece of wood above described.

During the last summer I made use of a thermometer with a fine tube, in which I found it difficult in some situations readily to mark the station of the quicksilver. I placed white paper behind the tube with some advantage, till it occurred to me to put a stripe of thick black paint upon the back of the tube, the breadth of which was about ⅙ only of the tube’s circumference. The optical effect of this was curious enough; for though the place of the black paint could scarcely be seen when the thermometer was viewed sideways; yet in front the whole of the glass appeared as dark as ink. The result was that the quicksilver losing no rays of light, and the tube within having much less luminous reflection than before, I could in many situations of the light and of the thermometer, discover the thread of quicksilver to much greater advantage than usual. I take the liberty to add to my packet through Coll. Smith, a thermometer on which this operation has been performed. I find that another device practiced upon thermometers with the same view, has been to flatten the bore in which the thread of the quicksilver lies, in order to increase the breadth of the thread to the eye; the advantage of which operation I have never had an opportunity of ascertaining; but I know that some who have used it, have since laid it aside. The most advantageous view that can be had of the thread of the thermometer, is certainly by bringing in light upon the tube from the back of its scale, or using a scale that is transparent, or by marking the degrees upon the tube itself; but as it is not always practicable thus to bring in the light from behind, I think that to some persons and in some cases the contrivance of the paint abovementioned may be of use. Indeed I am not sure whether it may not in some measure be combined with the use of the slit in the scale, so as to allow of both advantages in the instrument at different moments. I have sometimes thought also, that if the polish were removed from some parts of the glass tube, it might produce some good effect. But my time does not allow me to try many experiments.

If I suspend the execution of what respects the hygrometer you have desired to be sent to you, till you repeat your directions on the subject, I hope you will not be put to any disappointment by the liberty I take in this particular.

With very great respect & esteem, I have the honour to be your Excellency’s most obedient and most humble servant,