Observations July 31. At one P.M. the Start bore W. N. W. distant six leagues. August 1. The water appears luminous in the ship's wake. — 2. The temperature of the water is taken at eight in the morning and at eight in the evening. - 6. The water appears less luminous. -7. Formegas S. W. distant 32 degrees. St. Mary's S. W. S. 33 leagues. 8. From this date the temperature of the water is taken at eight in the morning and at six in the evening. 10. Moonlight, which prevents the luminous appearance of the water. 12. Ditto. From this date the temperature of the air and water was taken at noon, as well as morning and evening. 24. The water appeared luminous in a small degree before the moon - 29. No moon, yet very little light in the water. 30. Much gulf weed to-day. 31. Ditto. September 1. Ditto. -2. A little more light in the water. - 6. Little light in the water. A very hard thunder-gust in the night. - 9. Little gulf weed. Little light in the water last evening. 10. Saw some beds of rock-weed; and we were surprised to observe the water six degrees colder by the thermometer than the preceding noon. This day (10th) the thermometer still kept descending, and at five in the morning of the 11th, it was in water as low as 70, when we struck soundings. The same evening the pilot came on board, and we found our ship about five degrees of longitude a-head of the reckoning, which our captain accounted for by supposing our course to have been near the edge of the Gulf Stream, and thus an eddy-current always in our favour. By the distance we ran from September 9th, in the evening, till we struck soundings, we must have then been at the western edge of the Gulf Stream, and the change in the temperature of the water was probably owing to our suddenly passing from that current into the waters of our own climate. On the 14th of August the following experiment was made. The weather being perfectly calm, an empty bottle, corked very tight, was sent down 20 fathoms, and it was drawn up still empty. It was then sent down again 35 fathoms, when the weight of the water having forced in the cork, it was drawn up full; the water it contained was immediately tried by the thermometer, and found to be 70, which was six degrees colder than at the surface; the lead and bottle were visible, but not very distinctly so, at the depth of 12 fathoms; but, when only 7 fathoms deep, they were perfectly seen from the ship. This experiment was thus repeated September 11th, when we were in soundings of 18 fathoms. A keg was previously prepared with a valve at each end, one opening inward, the other outward; this was sent to the bottom in expectation that by the valves being both open when going down, and both shut when coming up, it would keep within it the water received at bottom. The upper valve performed its office well, but the under one did not shut quite close, so that much of the water was lost in hauling it up the ship's side. As the water in the keg's passage upwards could not enter at the top, it was concluded that what water remained in it was of that near the ground; and, on trying this by the thermometer, it was found to be 58, which was 12 degrees colder than at the surface. [This last Journal was obligingly kept for me by Mr. J. Williams, my fellow-passenger in the London Packet, who made all the experiments with great exactness.] 1598. TO JAN INGENHOUSZ1 ON THE CAUSES AND CURE OF SMOKY CHIMNEYS DEAR FRIEND, (L. L.) At Sea, August 28, 1785 In one of your Letters, a little before I left France, you desire me to give you in Writing my Thoughts upon the Construction and Use of Chimneys, a Subject you had sometimes heard me touch upon in Conversation. I embrace willingly 1 This letter, which has been published in a separate pamphlet, both in England and America, first appeared in the Transactions of The American Philosophical Society, Vol. II, p. 1 (1786), in which it was read October 21st, 1785.- ED. this Leisure afforded by my present Situation to comply with your Request, as it will not only show my Regard to the Desires of a Friend, but may at the same time be of some Utility to others; the Doctrine of Chimneys appearing not to be as yet generally well understood, and Mistakes respecting them being attended with constant Inconvenience, if not remedied, and with fruitless Expence, if the true Remedies are mistaken. Those who would be acquainted with this Subject, should begin by considering on what Principle Smoke ascends in any Chimney. At first, many are apt to think, that Smoke is in its Nature and of itself specifically lighter than Air, and rises in it for the same reason that Cork rises in Water. These see no Cause why Smoke should not rise in the Chimney, tho' the Room be ever so close. Others think there is a Power in Chimneys to draw up the Smoke, and that there are different forms of Chimneys, which afford more or less of this Power. These amuse themselves with searching for the best Form. The equal Dimensions of a Funnel in its whole Length is not thought Artificial enough, and it is made, for fancied Reasons, sometimes tapering and narrowing from below upwards, and sometimes the contrary, &c. &c. A simple Experiment or two may serve to give more correct Ideas. Having lit a Pipe of Tobacco, plunge the Stem to the Bottom of a Decanter half fill'd with cold Water; then putting a Rag over the Bowl, blow thro' it and make the Smoke descend in the Stem of the Pipe, from the End of which it will rise in Bubbles thro' the Water; and, being thus cool'd, will not afterwards rise to go out thro' the Neck of the Decanter, but remain spreading itself and resting on the Surface of the Water. This shows that Smoke is really heavier than Air, and that it is carried upwards only when attach'd to, or acted upon, by Air that is heated, and thereby rarefied and rendered specifically lighter than the Air in its Neighbourhood. Smoke being rarely seen but in company with heated Air, and its upward Motion being visible, tho' that of the rarefied air that drives it is not so, has naturally given rise to the Error. I need not explain to you, my learned Friend, what is meant by rarefied Air; but if you make the public use you propose of this Letter, it may fall into the Hands of some who are unacquainted with the Term and with the Thing. These then may be told, that air is a Fluid which has Weight as well as others, tho' about 800 times lighter than Water. That Heat makes the Particles of Air recede from each other and take up more Space, so that the same Weight of Air heated will have more Bulk, than equal Weights of cold Air which may surround it, and in that Case must rise, being forc'd upwards by such colder and heavier Air, which presses to get under it and take its Place. That Air is so rarified or expanded by Heat may be proved to their Comprehension by a lank blown Bladder, which, laid before a Fire, will soon swell, grow tight, and burst. Another Experiment may be, to take a glass Tube about an Inch in diameter, and 12 Inches long, open at both Ends and fixed upright on Legs, so that it need not be handled, for the Hands might warm it. At the End of a Quill fasten 5 or 6 Inches of the finest light filament of Silk, so that it may be held either above the upper End of the Tube or under the lower End, your warm Hand being at a distance by the Length of the Quill. (Plate XIV. Fig. 1.) If there were any motion of Air thro' the Tube, it would manifest itself by its Effect on |