112 PHILOSOPHICAI- TRANSACTIONS. [anNO 1750, 



hour : which is near 1 8 times a greater velocity than that of the strongest storms ; 

 which is estimated to be at the rate of 50 miles in an hour. 



" Hence, we see that an outrageous hurricane may be caused, by destroying 

 a small proportion of the elasticity of the air of any place, in respect to the 

 whole. No wonder then that such violent commotions of the air should produce 

 hurricanes and thunder showers ; especially in the warmer climates ; where both 

 the sulphureous and watery vapours, being raised much higher, and in greater 

 plenty, cause more violent effects. 



" Monsieur de BufFon in his Natural History, and Theory of the Earth, men- 

 tions black dark clouds in the air near the tempestuous Cape of Good Hope, and 

 also in the ocean of Guinea, which are called by the sailors the Ox's Eye ; which 

 are often the forerunners of terrible storms and hurricanes. Whence it is to be 

 suspected, that they are large collections of sulphureous vapours ; which, by 

 destroying suddenly a great quantity of the elastic air, cause the ambient air to 

 rush with great violence into that vacuity, thereby producing tempests and hur- 

 ricanes. And off the coast of Guinea they have sometimes 3 or 4 of these hur- 

 ricanes in a day; the forerunners of which are these black sulphureous clouds, 

 with a serene clear air, and calm sea ; which on a sudden turns tempestuous, 

 on the explosion of these sulphureous clouds. And in Jamaica they never have 

 an earthquake when there is a wind to disperse the sulphureous vapours. 



" In like manner we find, in the late earthquakes at London, and in the ac 

 counts of many other earthquakes, that before they happen there is usually a 

 calm air, with a black sulphureous cloud : which cloud would probably be dis- 

 persed like a fog, were there a wind : which dispersion would prevent the earth- 

 quake ; which is probably caused by the explosive lightning of this sulphureous 

 cloud ; being both nearer the earth than common lightnings ; and also at a 

 time when sulphureous vapours are rising from the earth in greater quantity 

 than usual ; which is often occasioned by a long series of hot and dry weather. 

 In which combined circumstances, the ascending sulphureous vapours in the 

 earth may probably take fire, and thereby cause an earth-lightning ; which is 

 at first kindled at the surface, and not at great depths, as has been thought : 

 and the explosion of this lightning is the immediate cause of an earthquake. 



" It is in the like manner that those meteors, called falling stars, are sup- 

 posed to be kindled into a flame at the upper part of a sulphureous train, which 

 is kindled downwards into a flame, in the same manner as a fresh blown-out 

 candle is instantly lighted from another candle held over it at a distance, in the 

 sulphureous inflammable smoke of it. 



" I am sensible that it may seem improbable, that the ascending sulphureous 

 vapours in the earth should thus be kindled ; but since they are continually as- 

 cending through the pores of the earth, more or less, for many good and useful 



