PROTECTION FROM LIGIITNING. 39 



it emanates, seeming to issue from their interior. This is the 

 most common of all the forms. 



Those flashes of light unattended by thunder which illumine the 

 horizon for hours, at times, on summer evenings, have been 

 characterized as heat lightning, and are generally attributed to 

 reflection from the atmosphere of the lightning of clouds so 

 distant that the thunder cannot be heard. Sometimes this light is 

 diffused over the . entire heavens, the electricity of the clouds es- 

 caping in flashes too feeble to produce audible sound. Especially 

 may this occur when the air is moist, so that it conducts electricity 

 with tolerable facility, and yet resists its passage sufficiently to 

 develop a feeble light. It may here be remarked that the form 

 under which lightning is presented, whether zigzag, sheet or heat 

 lightning, depends upon the position of the observer. That which 

 may present itself as zigzag lightning to one observer, may appear 

 as sheet or heat lightning to another located differently. 



While the first form of lightning is that which will principally 

 engage our attention, yet, lightnings of the second class are so 

 unique in their manifestations, I can hardly resist the temptation 

 to draw examples of them from that part of the admirable 

 meteorological essays of Francois Arago which treats of thunder 

 and lightning.* Unlike the instantaneous flashes of the other 

 forms, lightnings of this class are visible for one, two, or even ten 

 seconds of time. Their movement in descending from the clouds 

 to the earth is so slow that their march can be followed by the 

 eye and their rate be estimated. They occupy definite spaces, 

 are of globular form, and are seemingly balls of fire. Against 

 them lightning conductors and all other means of protection 

 which man has devised, seem to be essentially powerless. 



We give below a few from the long list of examples referred to 

 above : 



" At Oouesnon, near Brest, among the ruins of a church which 

 had been entirely destroyed, different witnesses agreed in at- 

 tributing the catastrophe to ' three fiery globes, each three or four 

 feet in diameter which united, and then proceeded with a very 

 rapid course in the direction of the church.' " 



" In January, 1710, a thunderbolt fell on the tower of Schemnitz 

 in Hungary. Its form was that of a globe, and its size as large 

 as a cask." 



* While facts have been drawn from any available sources, I desire to acknowledge 

 particular indebtedness to the work referred to above. 



