CAN WE ALWAYS COUNT UPON THE SUN? 663 



ture, while primarily brought about by the condition of the sun, is 

 directly due to the action of local causes, and that in other parts 

 of the earth a simultaneous increase of heat may be experienced. 

 A very great increase of solar radiation, however, could not be 

 thus masked in its effects upon the earth. 



Although during the historical period there has probably been 

 no sufficient variation in the activity of the sun to produce very 

 serious terrestrial results, yet it is known that the sun-spot cycle 

 is subject to considerable variations, both as regards the length 

 of the periods and the intensity of the forces concerned in the 

 disturbance. The latest maximum of sun-spots in 1883-'84 was a 

 couple of years overdue. What peculiarities may mark the maxi- 

 mum now approaching time alone can reveal. But, at any rate, 

 the known irregularities of the sun suggest a striking resemblance 

 to what we see in some of the variable stars ; and it is highly prob- 

 able that the changes of the latter, except in certain cases where 

 other more satisfactory causes have been inferred, are due to 

 phenomena resembling sun-spots, if not in fact directly analogous 

 to them. Is sun-spottedness, then, a progressive condition ; and 

 will our sun in time become, through this cause, variable to the 

 extent shown by many of its compeers in the heavens ? 



It is true that on account of the remoteness of any calamitous 

 effects resulting from such gradual changes in the sun's condition 

 we can afford to regard them with indifference, so far as the wel- 

 fare of our race for many thousands of years is concerned ; but 

 when we rise to a higher point of view, and put aside merely 

 human measures of time, the question becomes one of deep inter- 

 est, since it involves the probable ultimate fate of our planet as the 

 scene of the development and achievements of intelligent creat- 

 ures. Will the earth become a desert like its companion the moon 

 through the exhaustion of its vital forces and the disappearance of 

 its air and water, while the sun yet shines upon it with unfailing 

 splendor ; or will the end of terrestrial life be brought about by 

 the agency of the sun itself, either through the failure of the solar 

 energies, or through an overwhelming outburst of them ? These 

 questions are not the less interesting, and not the less certain to 

 obtrude themselves, because it is at present impossible for us to 

 answer them. They have also a bearing upon the geological life 

 record of the globe. Already, under the enormous demands for 

 time made by the evolutionary doctrine, geology is asking for far 

 longer periods of stability in the light and heat supplies of the 

 sun than astronomy, also supporting itself upon the 'principles of 

 evolution, is able to grant. But if the sun has emerged from the 

 stage of a third or fourth type star, and by the gradual elimina- 

 tion of its obstructive envelope has arrived at that point of com- 

 parative regularity of radiation in which we behold it, the time 



