liv Appendix. 



followed a period of eight or ten weeks during which the temperature was 

 above the mean, followed by another period of unusual cold. A careful 

 examination of such records as are available convinces us at once that such a 

 circumstance is no fortuitous accident. There is a weather cycle, not yet 

 perhaps so clearly defined, but certainly as well ascertained as any of those 

 cycles of celestial movements which depend on the unvarying law of gravita- 

 tion. The temperature of the earth's surface varies from year to year, and 

 shows a maximum every eleven years, or rather in periods of a little more 

 than eleven years. Just before the maximum, and just after it, come the 

 periods of lowest temperature. Very lately, Professor Smyth in Edinburgh, 

 Mr. Stone at the Cape of Good Hope, and Mr. Abbe at Cincinnati, each 

 working upon different materials, have pointed out the close coincidence 

 between the curve of varying terrestrial temperature and that of the sun-spot 

 periods ; this is the first generalization. Observations of the sun's surface 

 have not yet extended over a period sufficiently long to admit of a comparison 

 of the phenomena presented with that more extended cycle of about forty-one 

 yeai*s which M. Renou long ago deduced from his investigation of the records 

 of great winters. The connection between terrestrial variations of climate and 

 the sun-spot period being established, we at once desire to push our investiga- 

 tion a step further. If the character of our winters depends on the condition 

 of the sun's surface what is it that rules the latter phenomenon 1 Is the cause 

 within the sun itself, or may we look for it without 1 Analogy and the cyclic 

 character of the variations lead us to prefer the latter solution. The extra- 

 ordinary character of the weather of the last and preceding 'years, the recent 

 extension of our means of examining the surface of the sun, the unusual 

 magnifi.cence of certain auroral displays which have occurred during the period 

 I have under review to-night, have combined to direct the attention of 

 physicists to the inter-connection of various cosraical and terrestrial phenomena. 

 The result has been that every research leads to surer convictions of the inter- 

 dependence of natural phenomena ; whilst the further we push our investiga- 

 tions the more we feel that the ultimate cause of those phenomena eludes our 

 grasp. 



No natural phenomenon of modern times has evoked at the moment of its 

 occurrence a greater mass of scientific record and speculation than the aurora 

 which, on the night between the 4th and 5th of February last, astonished 

 Europe, and fired the skies over one-half the globe. This aurora was visible in 

 North America and the West Indies, over the whole breadth of Europe, in 

 "Western Asia, at the Mauritius, and in Western Australia. There can be 

 very little doubt that, had daylight not interfered to prevent it, the magnificent 

 spectacle which it presented would have been seen from every point on the 

 surface of the globe. 



