Memoir on the FoJJil Caout-^Chouc, ^c. 2 •2-5 



but from the 21ft of June to the i8lh of Auguft no part of it 

 will be feen, as its darkened fide during that period will be 

 turned towards the earth. This difappearance and reappear- 

 ance of Saturn's ring will be of importance to aftronomerSj as 

 it will enable them to determine the direftion of the plane pf 

 the ring, and will afford a curious fpeftacle to amateurs who 

 are provided with good telefcopes. The ring, which already 

 appears as a broad ftripe of light, will continually become 

 fmaller till the 15th of June; after which time it will difap- 

 pear till the 15th of Auguft, when it will appear as a fine 

 Itripe of light, which will increafe in breadth till the aper- 

 ture between it and the planet will increafe during the firft 

 feven years. As Saturn till the month of June fets at mid- 

 night, the decreafe of the ring may always be obferved ; but 

 when he fets earlier it will be poflfible to fee him only a fliort 

 time in Auguft, as he will be loft in the fun's rays. 



Leyden, 

 March 10, 1803. 



XL. Memoir on the FoJJil Caout-Chouc, or Elajiic Bitumen 

 of Derbyjhire, j^y Fauj as-Saint-Fond *. 



Ai 



.BOUT twenty years ago fome infulated portions of a 

 kind of blackifli bitumen, compreffible and even elaftic, which 

 had fome fort of refemblancc to old leather, were found in the 

 natural filfures of one of the mines of Caftleton. The young 

 miners having fet fire to fome of this matter, it burnt with a 

 bright flame, emitting an odour which did not appear to be 

 <Jifagreeablc. 



At that period mineralogy was not fo well known as at 

 prelent in England, and particularly in Derbylhire : no one 

 paid attention to this foHil, or endeavoured to afcertain its 

 nature. 



Twelve years after, a heavy ftorm of rain having produced 

 a deep ravine on the fide of one of the hills which furround 

 the village of Caftleton, a fimilar kind of bitumen was found 

 between the foffil ftrata of argillaceous fchift which exifts at 

 the bottom of that hill. 



More care was then taken to colleft this matter, fome of 

 which was fent to Derby, Edinburgh,, and London ; and fo 

 great a relation was found between it and the caout-chouCy 

 knov^n under the vulgar name (•<{ elajiic gum, that mineralo- 

 gifts did not hefitate to confider it as the fame as that brought 



• From Journal Ju Mufetim National, No. 4. 



Vol. XV. No. 59. Q^ from 



