276 LETTERS ON NATURAL MAGIC. 



1697, two troops of horse were dismounted and drawn tip 

 in line in order to fire their volleys. Opposite the centre 

 of the line was the door of a butcher's shop, where there 

 was a large mastiff dog of great courage. This dog was 

 sleeping by the fire, but when the first volley was fired, it 

 immediately started up, ran into another room, and hid 

 itself under a bed. On the firing of the second volley, the 

 dog rose, run several times about the room, trembling 

 violently and apparently in great agony. When the third 

 volley was fired, the dog ran about once or twice with 

 great violence, and instantly fell down dead, throwing up 

 blood from his mouth and nose. 



Sounds of known character and intensity are often 

 singularly changed even at the surface of the earth, accord- 

 ing to the state of the ground and the conditions of the 

 clouds. On the extended heath, where there are no solid 

 objects capable of reflecting or modifying sound, the 

 sportsman must frequently have noticed the unaccountable 

 variety of sounds which are produced by the report of 

 his fowling-piece. Sometimes they are flat and prolonged, 

 at other times short and sharp, and sometimes the noise 

 is so strange that it is referred to some mistake in the 

 loading of the gun. These variations, however, arise 

 entirely from the state of the air, and from the nature and 

 proximity of the superjacent clouds. In pure air of 

 uniform density the sound is sharp and soon over, as the 

 undulations of the air advance without any interrupting 

 obstacles. In a foggy atmosphere, or where the vapours 

 produced by heat are seen dancing as it were in the air, 

 the sound is dull and prolonged ; and when these clouds 

 are imm diately overhead, a succession of echoes from 

 them produces a continued or a reverberating sound. 

 When the French astronomers were determining the 

 velocity of sound by firing great guns, they observed that 

 the report was always single and sharp under a perfectly 



