Polytechnic Association. 703 



masses of various temperature coming together. The material for the 

 generation of gases is also present in the highest condition for the 

 operation of the electric currents — the watery globules expanded with 

 heat. Seasoning from the effect to the cause, we are brought to the 

 conclusion, that there are, in fact, immense volumes of Irvdrogen and 

 oxygen gases accumulated in the thunder clouds ; and that the electric 

 spark or lightning explodes them from time to time, with the astounding 

 reports and vivid flashes by which our nerves are so often shaken. It 

 is demonstrable that the volume of sound does not depend upon the 

 quantity or intensity of electricity set free. The heaviest thunder we 

 ever heard was not attended by the sharp rattling sound which 

 indicates a lightning stroke ; but it shook the house like an earthquake. 

 Such concussions prove the prodigious force of the explosion. The 

 circumstance to which we have already ar 1 . . erted, is to be considered 

 in estimating the sound of thunder, namely, that it descends. If we 

 were to imagine the largest ordnance ever cast to be discharged at 

 such a distance from and above us, the report would be insignificant 

 when compared to that of the loudest thunder. The successive peals 

 of thunder in a storm are of various degrees of loudness, the natural 

 effect of the varying dimensions of the volumes of gas that may be 

 exploded. Sometimes we hear redoubled reports, the second not 

 unfrequently being louder than the first, occasioned probably by the 

 lightning in its course firing two or more separate volumes of those 

 gases accumulated in different and remote sections of the clouds, and 

 those subsequently exploded being larger than the first. What is 

 called heat or sheet lightning, is not accompanied by thunder, at least 

 such as is audible to us either from the distance, or the small quantity 

 of gas exploded. 



All artificial development of electricity, by friction, gives out the 

 spark with a crackling sound, which is a miniature resemblance of 

 the clattering, crackling sound that the lightning is always observed 

 to produce when it passes very near to us through the air, and which 

 is altogether different from the loud detonation or the " repercussive 

 roar " succeeding it, that signalizes the heaviest thunder peals. The 

 prolonged reduplicated sound, which when reverberated is but an echo 

 of the original report, is so unlike that of the lightning, as we have 

 always heard it when very near, that we cannot believe it to be caused 

 by the passing of the lightning through the atmosphere ; and it is 

 only in this way that sound from lightning is caused, for its mere 

 elimination from the point whence it is discharged gives out no sound 

 as we suppose ; it is the resistance of the atmosphere to so intense a 



