TRANSACTIONS OF SECTION A. 925 
‘The glass globe has become a beautiful mirror by the fine particles of platinum 
that have been projected against it. 
N.B.—A separate earth-plate has since been put to the telephone, so that 
nothing of the kind can again happen. : 
18. On a supposed Periodicity of the Cyclones of the Indian Ocean south of 
the Equator. By Cuartes Metproum, F.R.S. 
In papers printed in the Reports for 1872, 1873, 1874, and 1876, I endeavoured 
to show that there were grounds for supposing that the cyclones of the Indian 
Ocean south of the equator increased in number, extent, and intensity from a 
minimum in one year to a maximum in another, and then decreased to a minimum, 
the period or cycle apparently corresponding with the eleven-year period of solar 
activity. 
From the data given in the last of those papers (Report for 1876, page 267) it 
would appear that from 1856 to 1875, the years of minimum cyclone-activity were 
1856 and 1867, and the years of maximum activity 186] and 1872, but that the 
results for each of those years did not differ much from the results for the year 
immediately preceding or following it, the variation near the turning-points being 
small. 
Before giving a brief outline of the results which have been obtained since 1875, 
it may be well to mention that the sources of information were the same as in 
former years. Two clerks were constantly occupied in tabulating the meteorological 
observations contained in the log-books of vessels that arrived in the harbour of 
Port Louis from different places. The number of days’ observations tabulated in 
each year, that is, observations extending over twenty-four hours, and made in 
different parts of the Ocean, was as follows :— 
Days’ Days’ 
Years Observations Years Observations 
STO. . i : rae ire ily LSS sy bas : Y «if, LOvtro 
Biles ; 2 wet, 006 LS8205" Jy, P Fs - 15,089 
BTS 1%. : : . 17,050 MASS). k at 2 ‘ ‘ t 16,930 
i : ! , 15,889 niko hs ¢ Swe aes 3 : . » 15,697 
1880. : : Sh OG 
The tables give an average of forty-six observations of twenty-four hours each 
for every day of the nine years over the frequented parts of the Ocean. 
All details and reports respecting hurricanes, storms, or gales, were recorded in 
separate registers. 
For each day on which there was a gale in any part of the Ocean between the 
equator and the parallel of 34°S. a chart was prepared, showing as nearly as possible 
the positions of the vessels, the direction and force of the wind &c. at a certain 
hour, viz., noon on the meridian of 60° E. 
From these synoptic charts, the details given from hour to hour in the log-books, 
and all the information obtained from other sources, the positions of the centres 
of cyclones at noon on each day were determined, and the tracks laid down on 
separate charts. 
Nine Cyclone-Track Charts have thus been prepared, since 1875, namely, one 
for each of the years 1876-84. 
These Track-Charts, together with the twenty that had previously been prepared 
for the years 1856-75 show, as far as has yet been ascertained, the tracks of the 
cyclones of the Indian Ocean south of the equator in each of the years 1856-84, 
and the tracks for the years 1848-65 are nearly ready. 
With respect to the period 1876-84, the areas of the cyclones and the distances 
traversed have not yet been determined, but upon the whole the nwmber and 
duration of the cyclones decreased to a minimum in 1880, and then increased till, in 
1884, they were more than double of what they were in 1880. 
From the accompanying Track-Charts for the eleven years 1856, 1857, 1860, 
1861, 1867, 1868, 1871, 1872, 1879, 1880, and 1884, it will be seen that the number 
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