OVER THE CITY OF PROVIDENCE, ETC. 299 



near for accurate observation. In one respect his narrative tends to 

 justify my opinion, that the exciting cause of tornadoes is electrical 

 attraction. In two instances in which flashes of lightning proceeded 

 from the water, Mr Allen remarked that the effervescence produced 

 by the tornado in the water very perceptibly subsided.* 



Extract from a Letter written hy Zachariah Allen, Esq,, of Providence. 



"It was about three o'clock, P. M., during a violent shower, that I 

 observed a peculiarly black cloud to form in the midst of light, fleecy 

 clouds, and to assume a portentous appearance in the heavens, having 

 a long, dark, tapering cone of vapour extending from it to the surface 

 of the earth. The form of this black cloud, and of the cone of vapour 

 depending from it, so nearly resembled the engraved pictures of ' water 

 spouts' above the ocean, which I had frequently seen, that I should 

 have come speedily to the conclusion that one of these ' water spouts' 

 was approaching, had I not been aware that this phenomenon occupied 

 a space in the heavens directly above a dry plain of land. Whilst at- 

 tentively watching the progress of the cloud, with its portentous dark 

 cone trailing its point in contact with the surface of the earth, I no- 

 ticed numerous black specks, resembling flocks of blackbirds on the 

 wing, diverging from the under surface of the clouds, at a great eleva- 

 tion in the air, and falling to the ground. Among these were some 

 objects of larger size, which I could discern to be fragments of boards, 

 sailing off obliquely in their descent. This alarming indication left 

 no room for doubt that a violent tornado w^as fast approaching, and 

 that these distant, dark specks were fragments of shingles and boards 

 uplifted high in the air, and left to fall, from the outer edge of the 

 black conical cloud. This fearful appearance was repeatedly exhibited, 

 as often as the tornado passed over buildings. 



"The whirlwind soon swept towards an extensive range of buildings, 

 within a few yards of me. the roof of which appeared to open at the 

 top, and to be uplifted for a moment. The whole fabric then sunk 

 into a confused mass of moving rubbish, and became indistinctly visi- 

 ble amid the cloud that overspread it, as with a mantle of mist. 



* See Essay on the Cause of Tornadoes or Waterspouts in sixth vol. American rhilo» 

 gophical Transactions, or in Silliman's Journal, vol. 32, for 1837. 



VI. — 3 z 



