The total rainfall at Port Louis, between the years 1855 and 1868 inclusive, is as follows:—
In _Rainfall._ _Condition of Sun._ 1855 42·665 inches Sun-spot minimum. 1856 46·230 „ 1857 43·445 „ 1858 35·506 „ 1859 56·875 „ 1860 45·166 „ Sun-spot maximum. 1861 68·733 „ 1862 28·397 „ 1863 33·420 „ 1864 24·147 „ 1865 44·730 „ 1866 20·571 „ Sun-spot minimum. 1867 35·970 „ 1868 64·180 „
I think no one, looking at these numbers as they stand, can recognize any evidence of a cyclic tendency. If we represent the rainfall by ordinates we get the accompanying figure, which shows the rainfall for eighteen years, and again I think it may be said that a very lively imagination is required to recognize anything resembling that wave-like undulation which the fundamental law of statistics requires where a cycle is to be made out from a single oscillation. Certainly the agreement between the broken curve of rainfall and the sun-spot curve indicated by the waved dotted line is not glaringly obvious. But when we strike an average for the rainfall, in the way adopted by Mr. Jeula for shipwrecks, how pleasantly is the theory of sun-spot influence illustrated by the Port Louis rainfall! Here is the result, as quoted by the high-priest of the new order of diviners, from the papers by Mr. Meldrum:—
Three minimum years—total rainfall 133·340 Three maximum years—total rainfall 170·774 Three minimum years—total rainfall 120·721
Nothing could be more satisfactory, but nothing, I venture to assert, more thoroughly inconsistent with the true method of statistical research.
May it not be that, underlying the broad results presented by Mr. Jeula, there are similar irregularities?
When we consider that the loss of ships depends, not only on a cause so irregularly variable (to all seeming) as wind-storms, but also on other matters liable to constant change, as the variations in the state of trade, the occurrence of wars and rumours of wars, special events, such as international exhibitions, and so forth, we perceive that an even wider range of survey is required to remove the effects of accidental peculiarities in their case, than in the case of rainfall, cyclones, or the like. I cannot but think, for instance, that the total number of ships lost in divers ways during the American war, and especially in its earlier years (corresponding with two of the three maximum years of sun-spots) may have been greater, not merely absolutely but relatively, than in other years. I think it conceivable, again, that during the depression following the great commercial panic of 1866 (occurring at a time of minimum solar maculation, as already noticed) the loss of ships may have been to some degree reduced, relatively as well as absolutely. We know that when trade is unusually active many ships have sailed, and perhaps may still be allowed to sail (despite Mr. Plimsoll’s endeavours), which should have been broken up; whereas in times of trade depression the ships actually afloat are likely to be, _on the average_, of a better class. So also, when, for some special reason, passenger traffic at sea is abnormally increased. I merely mention these as illustrative cases of causes not (probably) dependent on sun-spots, which may (not improbably) have affected the results examined by Mr. Jeula. I think it possible that those results, if presented for each year, would have indicated the operation of such causes, naturally masked when sets of four years, four years, and three years are taken instead of single years.