X CONTENTS. 



VII. An Account of the Principles and EfFe£l of Steam Engines, which a£l 

 by Means of a Pifton. With Defcriptions of the Atmofpherical Engine 

 of Newcomen and Cawley, the Engine of Watt, which works in Vacuo ; 

 and a new Engine by Mr. Sadler, m which the direft Aftion of Steam and 

 the Preflure of the Atmofphere are combined — — p. 22S 



Familiar defcription of the fteam-engine of Newicomen and Cawley j and of Watt and Boulton^ 

 Defcription and principles of Mr. Sadler'a (team engine. 



VIII. On the fuppofed Improvement of Achromatic Lenfes, when, rendered 

 more tranfparent by cementing them together — — ?• ^33 



Caufe of the obfciirity and mifty appearance of objefts through achromatic lenfes. Remedy by tb« in- 

 terpofition of water, and of maftic. Approved by feveral eminent French philofophers. Experiment 

 by W. N. Mr. Ramfden's account of a compound lens cemented together. The aberrations are 

 greatly increafed by this treatment, and the lens rendered lefs perfeft. 



IX. Defcription of a very fimple Apparatus for performing the great Ex- 

 periment of producing Water by the Combuftion of Hydrogen Gas, In-. 

 vented by Mr. John Cuthbertfon — — ■ — P- ^35 



Scientific News — — — — p« 236 



Account of the public fitting of the National Inftitute of Sciences and Arts, held at Paris, July 3, 

 1798. 



Mr. Dodd's projeft and eftimate for a tunnel, or fubtcrraneous road, under the Thames, from Grayef. 

 end to Tilbury. Remarks. 



Particulars of Dr. Herfchel's difcovery of four newfatellites to the Georgium Sidus. The old fatellites 

 move in a retrograde direftion, Surmife of two rings; and obfervation of the oblate figure of this 

 primary planet. 



SEPTEMBER 1798. 



Engravings of the following Objefts : i. An Apparatus for Bleaching by the 

 Oxygenated Marine Aci<i ; and, «. An Artificial Overflowing Well. 



I. Experiments on Carbonated Hydrogenous Gas, with a View to determine 

 whether Carbon be a Simple or a Compound Subftance. By Mr. William 



• Henry — — — — — p. 241 



Hxpanflon of carbonated hydrogenous gas by eleftrization, obferved by Dr. Auftin. Conclufion that 

 hydrogen is evolved : Queftion, whether this comes from the carbon ? Obfervations and experi- 

 ments to fliew that water is decompofed, and not the carbon ; which muft, therefore, ftill be con- 

 fidered as an elementary fubftance. 



II. Obfervations on Bituminous Subftances, with a Defcription of the Va- 

 rieties of the Elaftic Bitumen. By Charles Hatchett, Efq. F.R.S. Lond. 

 and Edin. S.L.S. &c. — — — — ' P- 248 



Trodu£tion of bitumens. New fpecies found in Derbyfliire, which is elaftic. Enumeration. Ex- 

 xerimcnts and obfervations on this fubftance. 



III. Ob- 



