«x 



CONTENTS. 



balls, on oppofite fides, were prefented two larger balls, which, by their attradion, drew the arm 

 afide. The arm, with its balU, was ioclofed in a wooden cafe, and the whole apparatus placed 

 tK a room adapted to this purpofe, and kept (hut while the obferver attended to the efFe£t from 

 without, by means of a (hort telefcopo oppofite each end of the bar. The power required t draw 

 the arm afide, was afcertained from the time of its free vibrations, and the denfity of the earth com- 

 puted from the comparifon between the effeft of its attraftion on the balls with the efFeift of the 

 fame nature by which the ai m was drawn from its ftationary pofition. This laft efftti amounted 

 to about one inch and a half when a thin wire was ufed, and about one third of an inch with a 

 thicker wire: the deviations were, therefore, very perceptible. The mean refult of the earth's 

 denfity proved to be 5,48 times that of water, 



VI. An Inquiry concerning the Chemical Properties that have been attri- 

 buted to Light. By Benjamin Count of Rumford, F.R.S. M.R.I. A. 

 (Concluded from p. 405.) — — — p. 4^3 



Reduftion of filver by means of charcoal in the humid way under the aftion of folar light, and 

 Jikewife by the heat of boiling water without light. Reduftions of gold by ether and folar light 

 — by etherial oil of turpentine and the heat of fteam. Oxydes of gold and filver reduced by 

 olive-oil in a fimilar procefs. Remarkable precipitation of the folution of gold upon magnefia 

 by folar light. 



VII. Some Account of the Perfian Cotton-Tree. By Matthew Guthrie, 

 M.D. F.R.S. &c. &c. — _ __ p. 4^7 



Account of various fpecies of cotton, particularly the Perfian cotton ; its cultivation and valuable 

 qualities. 



VIII. Fafts and Obfervations concerning the Meafure and Expence of firft 

 Movers, namely. Wind, Water, Steam, and Animal Strength, and on other 

 Objefts of general Utility. (W. N.) — — ■ p. 459 



Great wafte of labour and expence incurred by manufaflurers and others, for want of a knowledge 

 of the relative powers of men, horfes, and other firft movers. — Obfervation refpefting the 

 beneficial tendency of improvements in the application of thefe fortes. Power of wind- 

 mills. Horizontal mills. Water-wheels with inclined pallets. Inftruftions for meafuring the 

 quantity and power of ftreams of water. Explanation of the manner in which this power ope- 

 rates. Example in detail to afcertain the force of a flream to be applied to an underihot-wheel 

 to raife w,iter, to grind corn, or to perform the work of a certain number of men or horfes. En- 

 quiries refpefting the medi\im effe& of animal power. Overfhot-wheels. Eafy method of le- 

 velling to determine the fall of a ftream of water. 



IX. Enquiries concerning the Invention and Praflice of the Art of Hat- 

 making. — — — — — p. 467 



X. New Obfervations on the Method of producing very loud Fulminatlons 

 with various Bodies by Means of Phofphorus. By Citizen Brugnatelli. 



p. 468 



Experiments in which detonations were produced by placing a fmall portion of phofphorus ur n 

 various fubftances containing oxygen, and ftriking tHera with a hammer. Thtfe were nitr. re 

 of filver, oxygenated muriate of potalh, the nitrates of bifmuth and of mercury, common nitre, 

 the fulphates (which did not fu ceed) and certain metallic oxydes. Experiments in which fnl- 

 phur and charcoal were ufed inftead of phofphorus. Additions and remarks by Van Mons. 



Tunnel 



