METEOEOLOGY. 



OBSERVATIONS ON THUNDER AND LIGHTNING. 



BY STILLMAN MASTERMAN, 

 Weld, Franklin County, Maine. 



The following observations on the duration of peals of thunder 

 were made for the purpose of verifying an assumption of my own, 

 that the limit usually assigned to the continuation of the rolling of 

 thunder is too low. I find that in some instances the rolling sound 

 of the thunder lasts several seconds longer than what meteorologists 

 have generally given as its extreme duration. In observing the sound 

 accompanying discharges of atmospheric electricity, a great variety is 

 apparent, not only in duration, but also in intensity and general 

 character. It would be futile to attempt to give all the gradations 

 and tones under which this sound is presented to the ear ; but I find 

 that it is conveniently divisible into four general classes, as follows : 



1. That which commonly commences with not a very great force, 

 and increases, generally somewhat regularly, up to its maximum 

 intensity, and then decreases until reaching its termination. Some- 

 times the maximum occurs at or near the commencement of the sound, 

 and again as near its termination. This is the more common class of 

 thunder. 



2. That which commences with a sound of moderate force and con- 

 tinues throughout its entire duration with but a slight variation in 

 intensity. In the annexed tables of observations, peals of this class 

 are designated by the word " uniform.'" 



3. That which presents a sound alternately very loud and low, in 

 rapid succession ; sometimes having rapidly succeeding maxima and 

 minima during its whole continuation. I designate peals of this class 

 by the word ^'vibratory." 



4. This class comprises those claps of thunder wliich have but a 

 momentary duration, like the sound of a cannon, fired wliere nothing 

 can reflect the sound as an echo. I distinguish claps of this class by 

 the term ^^ momentary." 



In making the annexed observations, I used in most cases an ac- 

 curate solar clock beating seconds, by which to note divisions of time. 

 Selecting such a position near the clock as to have an unobstructed 

 view of the quarter of the heavens occupied by the storm, and to be 

 able to catch the least audible sound of thunder, I could count the 

 beats of the pendulum, either by the clicking, or, if necessary, by its 

 perceivable motion. In cases of peals of thunder preceded by visible 

 electric discharges, I commence to count the seconds from the flashing 

 of the lightnino; ; notinsr the first audible instant of sound of the 

 thunder, its maximum intensity, and its last moment of audibility, 

 by marking their respective number of seconds from the instant of 

 visibility of the lightning. In peals not preceded by visible lightning 



