« CONTENTS. 



Portugal, eight ytar* ■befoie Celumbus, and difcoTcrcd Braxil and other parti of South Ameriea 

 Various collaLcial proofs. 



V. Analyfis of tlie Oriental Lapis Lazuli. By M. Klaprotk — p. 77 



Former expcnments cnumfrated. Analyfis. Blue colour not changed by ignition ;— but it become* 

 l>Ueifh grey with enamel. Other experiments in tlie dry and humid methods. Component parts 

 of ihe ftone. - 



VL Ufcful Notices refpcSing various Objefls — Rofe Water — Eau de Luce — 

 Soap of Wool— Sea Sicknefs — — — p. 80 



Rofe-water, how to be procured freth at all times. Eau de luce, experiments for making. Repetitioa 

 of Chaptal's operation for making foap of wool. Ether faid to be a cure for fea ficknefs. 



VII. A Comparifon bctw'&en Eleftrical Machines with a Cylinder, and thofe 

 which produce their Effeft by Means of a circular Plate of Giafs. With a 

 Defcripiion of a Machine of great Simplicity and Power, invented by Dr. 

 Martinus Van Marum — — — — P- 83 



Obfcrrations on the aftion of machines with a cylinder. Undulation of eleftrlcity. Defcription of 

 a machine with a plate of glafs exhibiting both powers. Numerical eftimatcs of the force of dif- 

 ferent elc£lrical machines. 



VIII. The Procefs for giving a beautiful White Colour to Raw Silk, without 

 Scouring. By M. Baume. (Concluded from page 32.) — p. 88 



Methods of recovering the alcohol after ofing it in bleaching — ^by adding alkali and dillilling— or bjr 

 diftillation alone. Inftrudlions. Difficulties of the new method of bleaching. Purification of 

 vitriolic acid. Proceft to obtain the marine acid. 



Mathematical Correfpondencc — — — P- 9^ 



Scientific News — — — ~* P* 93 



AnalyGi of the four firft cahicri of the Journal of the Polytechnic School. 



New Ptiblicaiions — — — — P- 95 



JUNE 1797. 



I. A Letter from Mr. dc Humboldt to M. Pidlet, on the Magnetic Po- 



larity of a Mountain of Serpentine — — — P- 97 



Situation and appearance of the mountain. ExperinKnts. Obfervation^ on the ftone which was 

 forwarded to Sir Jofeph Banks with the memoir. 



II. An Account of fome Experiments upon Coloured Shadows. By Lieutenant 

 General Sir Benjamin Thompfon, Count of Rumford, F. R. S. In a Letter 

 to Sir Jofeph Bank?, Bart. P. R. S. — — — p. loi 



Difference in colour between candle-light and day-light.— Obfervations. Expeiiments with coloured 

 gUflcs, candlci and lamps. Senfations of colour afforded by mere contrail. Intcreding e(fe£ls. 

 2 



