CONTENTS. iii 



MAY 1799. 



Engravings of the following Objc(fls : r. An Engine, by Roclion, for the fpecdy 

 and accurate engraving of IMIetallic Plates : and, 2. The Furnace for convert- 

 ing Bar-iron into Steel by Cementation. 



I. On the Philofophical Ufes of a common Pocket Watch. By the Rey. Wil- 

 liam Pearfon, - - - - - P- 49 



Utility of the common watch for meafuring fmall portions of time. Method of determinihg thofe 

 portions. Numbers propofed for a new watch to meafure Viours, minutes, feconds, and quarters, 

 without any extra wheel-work. Caution to medical men in the porchafe of a ftop-watch, on ac- 

 count of an impofition pradifed in the conftruflion of thofe inftrumeuts. 



II. A Letter from Mr. H. Davy, introduftorv to the Experiments contained in 

 the fubfequent Article, and on other Subjevfls relative to the Progrefs of 

 Science. - - - - - P- 55 



III. Experiments and Obfcrvations on the Silex compofing the Epidermis or ex- 

 ternal Bark, and contained in other Parts of certain Vegetables. By Humphry 

 Davy. - - - , - - - - P- 5^ 



Light produced by the coUifion of two pieces of bonnet cane againft each other, or againft filiceous 

 ftone or fteel. This phenomenon is not eleftric ; but arifes from filex in the epidermis of the 

 vegetable. A portion of the epidermis examined by calcination, fufion with alkali, folution in 

 water, and precipitation by muriatic acid : nearly two-fifths of filex were obtained. The wood 

 and inner bark of the cane afforded fcarcely any filex. Examination of other canes ; the EnglilH 

 reeds and grafTes, the hulks of wheat, &-c. all which afforded filex. The filex appears to be orga- 

 nically difpofed in vegetables. General remarks. 



IV. Analytical Table of the Refults of the Courfe of Experiments on the lateral 

 Communication of Motion in Fluids. By Citizen J. B. Venturi, Profeffor of 

 Experimental Philofophy at Modena, &c. Drawn up by the Author himfelf. 



P- 5Q, 



V. A Memoir on the Typographic Art. By Alexis Rochon, of the French 

 National Inftitute, and Diredtor of the Marine Obfervatory at the Port of 

 Breft. - - - - - p. 6r 



Encomium on the art of printing, with a flight profpefl of its origin. Printing by caft plates in re- 

 lief firft praftifed by William Ged of Edinburgh, in 1744. Obfervatiotis on this art and that 

 made ufe of by the Chinefe. Invention of Dr. Franklin for rautiplying the copies of hand-writ- 

 ing by a mechanical procefs of engraving. A neater procefs by the author, by means of counter, 

 proofs. 



Defcription of a machine for ftamping letters in a metallic plate, with great fpeed and precifion. 

 It confifls of an horizontal wheel which carries all the punches; a fcrcw to make the impreffion, by 

 afting on the head of the punch ; and a carriage to which the metallic plate is attached, and 

 which is moveable between each ftroke. according to the fpaces required between letters, words, 

 and lines. Report of the French Academy, and account of the expedients by which the neceffary 

 precifion and difpatch are infured. Stereotype method of printing. Method of taking impreffions 

 of coins in bell-metal by means of heat. The ancients ufed heat in their procefs of coining. 



b 2 VI. 



