SPONTANEOUS IGNITION OF CHARCOAL. g^7 



hama Channel. The English call it Chesterfield. There 

 is a small errour in the latitude of this Key, as given in our 

 Connoissance des Temps. In our voyage I ascertained it to 

 be 22° 7', instead of 21° 55'. The want of tolerable charts 

 of this dangerous part, and the necessity of comparing the 

 ship's place on the chart with sure data, render this observa- 

 tion interesting for those who sail without a pilot on board. 

 As to the longitude, it was agreeable to what I obtained 

 by the timekeepers. This key must not be confounded 

 with another of the same name on the south of the Great 

 Bank of Bahama, and almost in the same latitude. 



The accuracy of both of the observations here given I 

 have verified by comparison with two Spanish charts pub- 

 lished in 1779 under the ministry of Mr, Langara, and de- 

 rived from the Hydrographer's Office at the Havannah. 



I know not where the latitude and longitude of San Sal- San Salvador 

 vador, one of the principal cities of Brazil, in the Bay of 

 All Saints, are to be found. When we anchored in that 

 bay, Mr. Fonsera, Captain in the Portuguese navy, and 

 superintendant of that harbour, told me, that its latitude 

 was 13°. and its longitude 42° 25'. An English work, in the 

 hands of all the navigators of that country, gives them 12° 

 4&' and 41° 5'. So considerable a difference led me, to pay 

 as much attention tQ the subject as our short stay would 

 permit; and I had an opportunity of finding both by lunar 

 observations and the timekeepers, that its true longitude is 

 about 41° 5'. The latitude of point St. Antony I ascer- 

 tained by several observations to be 12° 59*8'. The time of 

 high water is twenty minutes after three, mean time. The Variation of 

 variation of the needle there in 1806 was 10° 20' E. the needle. 



IX. 



On the Spontaneous Ignition of Charcoal : by B. G. Sage, 

 Member of the Institute, Founder and Director of the 

 first School of Mines*. 



,R. de Caussigni appears to have been the first who f harco&l fired 

 observed, that charcoal was capable of being set on fire by in grinding, 

 tjie pressure of millstones. I 



* Journal de Pbvsique, vol. LXV, p. -423. 



Mr. 



