1853.] Geometrical Measurement of Barometric Waves. 77 



On a Geometrical Measurement of the distances from Crest to Crest 

 of the Barometric Waves in a Cyclone.— -By Henky Piddington, 

 President of Marine Courts. 



The measurement of the pressure of the Barometric Column, 

 whether arising from changes in its density or from actual variations 

 in its height ; such as the fish at the bottom of the sea must experi- 

 ence by the effect of every wave which rolls over them ; we have 

 possessed since the days of Torricelli and Pascal, and though, from 

 our ignorance of the definite extent of the atmosphere and other 

 causes, we can only express that pressure or vertical height by a con- 

 ventional scale, which expression again though depending always on 

 one fact, is different with different nations, we may still be said to 

 have a measure, though an imperfect one, of the height of the atmo- 

 spheric waves : assuming as we always do in using a Barometric mea- 

 surement that we know and allow for all the causes which influence 

 their density. 



That these variations in the Barometric pressure also succeeded 

 each other in the form of waves, at greater or less intervals of time, 

 so as to be traced over large areas, has of late years been well known, 

 and the attention of Meteorologists has been much directed to this 

 research, of which an illustrious professor of science has justly said — 

 " the great extent of country over which the accidental variations of 

 the Barometer take place is one of their most striking features, and 

 in a future and more advanced state of Meteorology, we may be able 

 to draw the most interesting and important conclusions from the 

 great atmospheric tidal waves which are thus perpetually traversing 

 oceans and continents."* 



"We also knew generally, and from undoubted authority, that the 

 Barometer both on the approach of, and during, Cyclones was subject 

 to very remarkable oscillations, but hitherto we have had no Barome- 

 tric measurements of their height, and though from their succession 

 in time we of course inferred that their crests were at a certain dis- 



* Professor Forbes' Report on Meteorology to British Association in 1832. 



