700 Transactions of the American Institute. 



thunder is remarkable. In the Penny Cyclopedia (article Thunder) 

 is to be found the following : " The identity of lightning with the 

 electric fluid is now well known ; but the physical detonation, which 

 accompanies the flash, is still the subject of conjecture ; in general it 

 is considered that lightning, by its heat, creates a partial vacuum in 

 the atmosphere ; that the sudden rushing of air into the void space 

 produces the sound; but various reasons have been assigned for its 

 prolongation. It was formerly supposed that the rolling noise is 

 merely the result of several echoes, caused by the sound being reflected 

 from mountains, woods, buildings or clouds, or from the latter alone 

 when a thunder storm takes place over the ocean. But though the 

 reflections of sound are very probably in part or at times the cause of 

 the prolongation of the report arising from the explosion, yet it must 

 be admitted that these will not always afford a satisfactory explana- 

 tion of the phenomena." 



In truth, there is as great a variety in the sounds of thunder as in 

 the flash of lightning or the direction and path of its motion. The 

 sights and sounds of a thunder storm are presented with such force 

 to our most observant senses, that, however men may differ in their 

 judgment as to the causes, their perception of the facts will be the 

 same ; the phenomena are upon so magnificent a scale, that they rivet 

 the attention and deeply impress the memory. Any true description 

 would be recognized as recalling to the mind the visible and audible 

 grandeur which such scenes have exhibited to all beholders. In deal- 

 ing with those facts there is, accordingly, the advantage of being cer- 

 tain that we are not misunderstood in relation to our perceptions of 

 the things we speak of; and, therefore, as in the search for the causes, 

 a knowledge of which is the chief desire of scientific pursuit— -felix 

 qui potuit rerum cognoscere causas — we have to speculate on some 

 facts which are not within the range of our senses. We shall not stop 

 to describe the various colors or kinds of lightning, the dimensions 

 of the sheet or flash, the lightning streak, chain lightning, or streams, 

 or their various directions, or the variety of sounds accompanying 

 them under the general name of thunder ; but take it for granted 

 that every reader has the same recollection of those sublime and beau- 

 tiful displays. 



The clouds are water in a state of vapor ; and water, composed of 

 the two gases oxygen and hydrogen, in the proportion of one volume 

 of the former weighing eight to two of the latter weighing one, is 

 subject to decomposition by currents of electricity, and to be converted 

 into those gases, its constituent elements. The operation is greatly 



