XIX. Aftronomical Obfervations. Communicated by David Ritten- XX. A Letter from Dr. Rittenhouse to Mr. Patterson, relative to a method of finding the fum of the feveral powers of the Sines, &c. XXI. Index Florae Lancaftrienfis, auctore Henrico Muhlenberg, D. D. XXII. Investigation of the Power of Dr. Barker's Mill, as improved by James Rumfey, with a description of the Mill, by W. Waring. 185 XXIII. A Thermometrical Journal of the temperature of the Atmos phere and Sea, on a voyage to and from Oporto, with explanatary obfervations thereon, to David Rittenhouse, L. L. D. President of • XXV. A Letter from Major Jonathan Heart, to Benjamin Smith Barton, M. D. Containing obfervations on the Ancient Works of Art, the Native Inhabitants, &c. of the Western Country. XXVI. An Account of fome of the principal Dies employed by the North American Indians. Extracted from a paper, communicated by the XXVII. An Account of the beneficial effects of the Caffia Chamacrista in recruiting worn-out lands, and in enriching fuch as are naturally poor: together with a botanical defeription of the plant. By Dr. James Greenway, of Dinwiddie-County, in Virginia. XXVIII. An Account of a Hill, on the borders of N. Carolina, fup- pofed to have been a Volcano. In a Letter from a Continental Of- ficer, refiding in that neighbourhood, to Dr. J. Greenway, near XXIX. An Account of a poisonous plant, growing spontaneously in the fouthern part of Virginia. Extracted from a paper, communicated N°. XXX. Defcription of a Machine for measuring a ship's way: in a Let- ter from Francis Hopkinfon, Efq. to Mr. John Vaughan. XXXI. An Inquiry into the Queftion, Whether the Apis Mellifica, or True-Honey-Bee, is a native of America. By Benjamin Smith XXXII. An Account of a Comet, in a Letter to Mr. R. Patterson, XXXIII. Cadmus, or a Treatife on the Elements of Written Language, py. With an Essay on the mode of teaching the Surd, or Deaf and confequently Dumb, to Speak. By Wm. Thornton, M. D. Hon- ored with the Magellanic Gold Medal, by the Philofophical Society, Page 261. XXXV. An Improvement on Metalic Conductors or Lightning-rods; in a Letter to Dr. David Rittenhouse, Prefident of the Society, from Robert Patterson of Philadelphia. Honored with the Magel- lanic Premium, by an Award of the Society in December 1792. XXXVI. An eafy and expeditious method of diffipating the noxious Va- pour commonly found in Wells and other fubterraneous places; by XL. Defcription of a SPRING-BLOCK, defigned to affift a Vessel in failing. By Francis Hopkinson, Efq. of Philadelphia. Honor- ed with the Magellanic Gold Medal, by an Award of the Society XLI. A Botanical defcription of the PODOPHYLLUM DIPHYLLUM of Linnæus, in a Letter to Charles Peter Thunberg, M. D. Knight of the Order of Wafa, Professor of Medicine and Botany in the University of Upfal, &c. &c. XLII. Obfervations on the conftruction of Hofpitals, by Mr. Le Roy. Member of the Royal Academy of Sciences.-(Extracted from an Effay on the fubject, which, with feveral elegant plans, was tranf- mitted by the author to the Society, but could not be inferted entire, as it contained many remarks of a local nature, refpecting Paris only. for. Page 194. after the Title of the piece No. 23. read To David Rittenhoufe, L. L. D. 247, line 16 for spot, read pot. Page 251, line 4, for the, read they. TRANS- 14 TRANSACTIONS OF THE American PHILOSOPHICAL SOCIETY, &c. N. I. Conjectures concerning the formation of the Earth, &c. in a letter from Dr. B. Franklin, to the Abbé Soulavie. SIR, Read Nov. 21, 1788. I Paffey, September 22, 1782. RETURN the papers with fome corrections. I did not find coal mines under the Calcareous rock in Derby Shire. I only remarked that at the lowest part of that rocky mountain which was in fight, there were oyster fhells mixed in the ftone; and part of the high county of Derby being probably as much above the level of the fea, as the coal mines of Whitehaven were below it, feemed a proof that there had been a great bouleverfement in the surface of that Island, some part of it having been depreffed under the fea, and other parts which had been under it being raised above it. Such changes in the fuperficial parts of the globe feemed to me unlikely to happen if the earth were folid to the centre. I therefore imagined that the internal part might be a fluid more dense, and of greater specific gravity than any of the folids we are ac A quainted quainted with; which therefore might fwim in or upon that fluid. Thus the furface of the globe would be a fhell, capable of being broken and difordered by any violent movements of the fluid on which it refted. And as air has been compreffed by art fo as to be twice as denfe as water, in which cafe if fuch air and water could be contained in a strong glafs veffel, the air would be feen to take the lowest place, and the water to float above and upon it; and as we know not yet the degree of denfity to which air may be compreffed; and M. Amontons calculated, that its denfity increafing as it approached the centre in the fame proportion as above the furface, it would at the depth of leagues be heavier than gold, poffibly the denfe fluid occupying the internal parts of the globe might be air compreffed. And as the force of expansion in denfe air when heated is in proportion to its denfity; this central air might afford another agent to move the surface, as well as be of use in keeping alive the fubterraneous fires: Though as you obferve, the fudden rarefaction of water coming into contact with thofe fires, may also be an agent fufficiently strong for that purpose, when acting between the incumbent earth and the fluid on which it refts. If one might indulge imagination in fuppofing how fuch a globe was formed, I should conceive, that all the elements in feparate particles being originally mixed in confufion and occupying a great fpace, they would as foon as the almighty fiat ordained gravity or the mutual attraction of certain parts, and the mutual repulsion of other parts to exift, all move towards their common centre: That the air being a fluid whose parts repel each other, though drawn to the common centre by their gravity, would be denfeft towards the centre, and rarer as more remote; confequently all matters lighter than the central part of that air and immerfed in it, would recede from the centre |