78 Geometrical Measurement of Barometric Waves. [No. 1. 



tance from each other in space, we had no sort of index as to what 

 that distance might be. In the present paper I have, as will be 

 seen from its title, the pleasure to announce an instance in which, by 

 the aid of Cyclonology, the Barometric waves of a Cyclone during its 

 passage have been, I think, accurately measured, both vertically by 

 the Barometer scale, and horizontally in geographical miles, giving 

 us thus, as in the beautiful instance of the Charles SeddWs Cyclone, 

 a new insight into the internal economy of these wonderful and 

 fearful phenomena, and, I hope for Meteorologists in general, a step- 

 ping stone of which we can only at present anticipate the advantage 

 from its position and the authenticity of its data. 



After a Cyclone from the 2nd to the 5th of May 1851, which 

 raged principally between Trincomalee and Madras, extending to 

 about 85° East Longitude — and which I have named " The Fox's 

 Cyclone" from H. M. S. Fox having made very bad weather by get- 

 ting too close in towards the centre before she bore up — I received 

 from my friend Capt. Chas. Biden, Master Attendant at Madras, 

 amongst a large collection of logs and other data some ten-minute 

 readings of the Barometer at the Madras Observatory. This was 

 what I had been long looking and hoping for from some quarter, 

 knowing, as I did, to what it might lead us if a complete short series 

 of Barometric observations in the track or neighbourhood of a 

 Cyclone could be obtained, together with the necessary data for an 

 accurate track of the Cyclone itself ; and having written to Captain 

 Biden on the subject, the Hon. Co.'s Astronomer, W. S. Jacobs, Esq. 

 was good enough to furnish me with a complete table of his ten- 

 minute readings extending from 8h. 41' a. m. on the 2nd May, to 

 llh. 41' on the 5th ; and from these, combined with the track of the 

 Cyclone which I was fortunately enable to trace very accurately, 

 having no less than twenty-six logs and reports. (See Journal 

 Vol. XXI. p. 283,) the accompanying Diagram which, it will be 

 seen, shows both the vertical height on the Barometric scale, and the 

 horizontal distance in miles and tenths from Crest to Crest of the 

 Barometric waves in the Cyclone, has been constructed. 

 To understand the plate it will be necessary to observe — 

 1. That, as shewn in the Diagram A. which is from the 

 Chart to the Memoir on this Cyclone, above quoted, omitting 



