44 BOARD OF AGRICULTURE. 



the case of thunder is due to the fact that the points along the 

 line of the flash are at unequal distances from the observer, a 

 separate sound being produced at each point. The sound from 

 the nearest point first reaches the ear, and then the sounds from 

 points more and more remote in order. If the relation of the line 

 of flash to the observer be such that two or more points are 

 equally distant, the sounds arising from these points blending to- 

 gether at the ear, will give a result proportionally louder, and thus 

 in nearly every peal of thunder maximum and minimum sounds 

 may be observed. Generally after a low rumbling sound for five 

 or ten seconds, a loud crashing sound occurs which continues 

 from five to twenty seconds, when it is succeeded by the rumbling 

 noise again which gradually dies away. Several maxima and 

 minima of sound may occur during the same thunder peal. The 

 rolling of thunder is also undoubtedly due in a considerable 

 degree to the effect of echoes. A cannon fired under a clear sky 

 gives a short, sharp cracking sound, but when fired beneath clouds 

 from which reflection can take place, the sound becomes pro- 

 longed and rolling. 



To consider in detail the questions : Does lightning ever occur 

 without thunder and with a clear sky ? Is thunder ever heard in 

 perfectly clear weather ? Does lightning take place without 

 thunder, with a cloudy sky ? Does thunder ever occur without 

 lightning ? would be foreign to our present purpose. It may 

 be remarked however, that seemingly well authenticated examples 

 are on record which would give an affirmative answer to each of 

 the above inquiries. Let us now turn our attention from these 

 general points in regard to lightning and thunder to those in 

 which Ave have a more specific interest. 



Other circumstances being equal lightning strikes the most 

 elevated points. Particular instances may occur which seem to 

 be in opposition to this rule — instances in which the causes re- 

 main concealed in the masonry of buildings or beneath the surface 

 of the earth. Yet, no one who has compared in a given locality 

 the strokes of church spires and tall trees with those of lower 

 surrounding objects will question the truth of the above state- 

 ment. 



Lightning seeks by preference metallic bodies, whether external 

 or concealed, and it is in making its way to them, or at the 

 moment of quitting them that it does its principal damage. Of 

 all the properties of lightning these are the most important to us 



