DIRECT AND AND INDIRECT BAROMETRIC WAVES. 277 



DIRECT AND INDIRECT BAROMETRIC WAVES. 



C. A. SHAW, ERIE, PA. 



The barometric disturbance which accompanied the volcanic eruption of the 

 island of Krakatau August 27, 1883, seems to deserve and doubtless will receive 

 exceptional consideration from meteorologists. 



Briefly, the narrative is that early in the morning of this date there occurred 

 a gigantic explosion, heard for a long distance, which tore the island apart, 

 threw an immense fragment a distance of some seven miles, probably producing 

 a new island, and started an immense tidal movement which is believed to have 

 journeyed around the world four times. "While the tidal gauges have recorded 

 their story the delicate fingers of the barometrical registers of the world have also 

 borne uninfluenced testimony of a similar kind. The blow which hurled such a 

 mass of matter into the air, which originated a hurricane there and caused the 

 barometers in the neighborhood of the volcano to rise and fall with unparalleled 

 rapidity, and a vessel, distant three hundred miles, to tremble, started an atmos- 

 pheric wave also around the globe. It was first detected in the Kew registers, 

 and the dates at which the atmospheric undulations passed various places on the 

 earth's surface it has been able to fix in many cases." 



"Two waves, one to the east and one to the west, started from Krakatau, 

 whose rate of progress has been fiund to be that of sound. ' ' 



The point to which I wish to call attention is that contained in these last 

 words, which I have italicized. It grves the first standard of measurement so far 

 as I am aware, of the rate of speed that a barometric wave travels under normal 

 conditions. Other observations have shown such variable speeds that we must 

 conclude either that their method of progression, as well as of occasion, is decid- 

 edly different from normal waves of propulsion or else that it requires an excep- 

 tional size of such air-wave to accomplish a rate of progress which shall be uni- 

 form and comparable to a standard, as that of the movement of sound. 



The barometer, it is said, rose and fell many tenths of an inch in a minute. 

 The rapidity of oscillation is possibly in this case as important as the range, for it 

 implies the power of the impulse to overcome the resisting medium in front and 

 the vibratory action of the surrounding atmosphere in quickly seeking to restore 

 its equilibrium. 



Future comparison of meteoric registers will determine several important 

 relations of a local and general character. For example, at that rate of speed it 

 undoubtedly overtook and passed certain areas of atmospheric low and high ba- 

 rometer producing conflicts of a peculiarly interesting nature. Some places must 

 have shown surprising barometric registering, though by the present detached 

 method of making observations it is but by chance that records of the Signal Ser- 

 vice at any station would show it. Self-registering instruments are needed. 



Were the service under any other direction than that of military men, it 



