CONNEXION OF CYCLONES AND RAINFALL WITH SUN-SBoTS. 219 
ber of cyclones, but their duration, extent, and energy were also much greater 
in the former than in the latter years, and that there is a strong probability 
that this cyclonic fluctuation has been coincident with a similar fluctuation 
of the rainfall over the globe generally. 
The present communication is confined to the twelye years 1856-67, 
comprising a complete sun-spot cycle. 
With regard to the cyclones of the Indian Ocean, the investigation is based 
upon the extensive collection of observations made by the Meteorological 
Society of Mauritius, on the assumption that the observations are so numer- 
ous that no cyclone of any considerable extent or violence can have escaped 
detection. 
A chart has been prepared for noon on each day of the period during 
which a cyclone lasted. The chart shows the positions of the vessels, the 
direction and force of the wind, the state of the weather and sea, &c. In 
this way the position of the centre of the cyclone is ascertained for each 
day, Then, by examining the several charts, the duration, extent, &c. of 
the cyclone are determined. 
- The number of cyclones thus examined for the twelve years is one hundred 
and thirteen, and their tracks have been laid down on six charts, 
The results of the investigation are given in Table IJ. Column 1 shows 
the dates; 2, the number of cyclone on chart; 3, the distance traversed ; 
4, the mean radius of cyclone; 5, area of cyclone, or x77; 6, the duration in 
days; and 7, total cyclonic area, or Dzr*, 
From Table I. we obtain the following general results :— 
2 
Number| Total | Sum | gi. o¢ |Dura-| Sumof | parts ated id 
Years.| of cy- | distance | of areas, ({io,in} total CNA. FORE ment 
clones. | traversed. | radii. * | days. | — areas. AFEAR, | || SUn-SRe 
numbers. 
miles. | miles.| sq. miles. 
i856. 6 850 815 | 856,468:5} 20 | 1,221,931:0 1:00 4:2 
1857. 5 1850 740 | 354,820:0| 19 | 1,270,130-0 1:04 | 21:6 
1858.; 12 3880 1656 | 75,2158; 389 | 2,890,781-7 2:37 50:9 
1859.) 14 5640 2026 |1,107,440-4| 48 | 4,809,189-9 394 | 96-4 
1860.| 13 8054 | 3131 |2,620,929:9| 61 |13,616,789:7|; 11:14 | 986 
1861.| 12 8730 2861 |2,849,552:1| 72 |14,937,699-7| 12-23 74 
1862.| 14 6140 2968 |2,406,879°1| 57 |11,370,279-7 9°53 59-4 
1863. 9 6320 | 2137 |1,590,155°7| 49 | 7,550,447-3 618 | 444 
1864. 7 4920 1341 | 876,628:5| 86 | 4,893,009°5 4:00 46:9 
1865. 8 3970 1426 | 904,150-4/ 28 | 3,396,409°1|. 2°78 30°5 
1866. 8 3130 960 | 509,961°2| 44 | 2,762,221-2 2°26 16:3 
1867. 6 2280 | 881 | 414,985:°5|} 27 | 1,913,845-5 1:57 73 
The total cyclonic area in 1860 and 1861 was about twelve times greater 
than in 1856 and 1857, and nearly eight times greater than in 1867. 
In short, all the factors were greatest in the years of maximum sun-spot 
frequency. 
It will be noticed that the cyclonic area increased rapidly from 1858 to 
1860, and diminished slowly from 1861 to 1866. qs 
The registers for the years 1856, 1857, 1866, and 1867 have been exa- 
mined with special care in order that nothing might be omitted; and to 
give the utmost possible weight to those years, every instance of even an 
ordinary gale has been taken into account. 
In 1856 there was no great hurricane at all; and the same may be said 
of 1857, 1866, and 1867. 
