1853.] Geometrical Measurement of Barometric Waves: 81 



The mean distance in geographical miles from crest to crest of 

 each wave is 5.91 miles. 



But if we take only the means of the ten hours and ten minutes 

 for which we have the actual track measured at sea, the means will 

 then stand as follows : 



Mean time of Transition of each wave Ih. 1'. 



Mean distance from crest to crest of each wave 4.62 miles. 



We may thus for the present say that — 



1. In a Cyclone of average violence (for this was by no means 

 an excessively violent one) travelling at the rate of 182.4 miles in 

 24h., or 7.6 miles per hour, there is a succession of aerial undulations 

 affecting the Barometer to the average extent of 0.020 per hour of 

 pressure, these being -f- or — according to the position of the centre, 

 and the curve of the undulation as shewn in the Diagram. 



2. That these variations of pressure occur at average intervals 

 of Ih. 4', and that their crests are at a horizontal distance of about 

 5 miles from each other ; the greatest horizontal distance being at 

 14.97 miles, and at the centre of the Cyclone, and the least at 1'.07 

 miles. 



As an Appendix to this paper, and because, however carefully the 

 original drawings are made, we cannot in India have them accurately 

 lithographed, and the unequal stretching and drying of the paper 

 again always deranges the most exact work in the printing. I 

 give here 



Table I. The Madras observations complete, as sent to me, for 

 the time included in the Diagram C, i. e. from 4 p. m. on the 4th 

 May to 1 a. m. on the 5th May, 1851, as being those from which 

 the projection is made. 



Table II. (2) The separate times at which the various undu- 

 lations passed over Madras, with (3) the intervals of these times. 

 (4) The heights the Barometer, and (5) their variations. (6) The 

 distances of the centre from Madras at these times ; (7) its bearing 

 (8) the angles of variation of bearings. (9) Distance, and (10) the 

 corrected distance in geographical miles from crest to crest of 

 each aerial wave of the Cyclone. 



U 



