54 



NATURE 



[March io, 1910 



atmosphere. Under the laws of molecular activity these 

 two atmospheres must be interchanging molecules at rates 

 dependent on the conditions of equilibrium between them. 

 It is reasonable that an excess in the earth's atmosphere 

 should cause it to feed out into the sun's sphere of control 

 more than it receives, and that a deficiency in the earth's 

 atmosphere should cause more feeding in from the sun's 

 supplementary atmospheres than the earth gives out. If 

 this conception be true and be efficient, the maintenance of 

 the delicate atmospheric conditions required for the con- 

 tinuity of life is automatically secured. . The failure of our 

 atmospheric supply is thus made to hang, not simply on the 

 losses and gains at the earth's surface, but on the solar 

 interchange, and hence on the solar endurance. 



The sun is giving forth daily prodigious measures of 

 energy. The endurance of the sun is not, however, merely 

 a question of unrequited loss, for it gains energy and sub- 

 stance daily as well as loses, and, so far as present 

 knowledge goes, its gain is greatly inferior to its loss. So 

 long as the heat of the sun was supposed to be dependent 

 on ordinary chemical changes, or on the fall of meteorites, 

 or on self-contraction, an activity adequate for terrestrial 

 life could only be estimated at a few million years. But 

 recent discoveries in radio-activity have revealed sources of 

 energy of an extremely high order. In the light of these 

 the forecast of the sun's power to energise the activities of 

 the atmosphere dependent on it, and to warm the earth, is 

 raised to an indeterminate order of magnitude. 



If we may thus find grounds for a complacent forecast in 

 reciprocal actions on the earth and in reciprocities between 

 the earth and the sun, are we free from impending dangers 

 in the heavens without? 



Present knowledge points to one tangible possibility of 

 disaster — collision with some celestial body, or close 

 approach to some sun or other great mass, large enough to 

 bring disaster by its disturbing or disruptive effect.*. 

 Within the solar system, the harmonies of movement 

 already established are such as to give assurance against 

 mutual disaster for incalculable ages. Comets pursue 

 courses that might, theoretically at least, bring about 

 collision, but do not appear usually to possess masses 

 sufficient to work complete disaster to the life of the earth 

 even should collision occur, whatever local disaster might 

 follow at the point of impact. The motions of the stars, 

 however, lie in diverse directions, and collisions and close 

 approaches between them are theoretically possible, if not 

 probable, or even inevitable. There are also in the heavens 

 nebulae and other forms of scattered matter, and doubtless 

 also dark bodies, which may likewise offer possibilities of 

 collision. The appearance of new stars flashing out sud- 

 denly and then gradually dying away suggests the actual 

 occurrence of such events. It has been even conceived that 

 the close approach of suns is one of the regenerative pro- 

 cesses by which old planetary systems are dispersed and 

 new systems are brought into being. One phase of the 

 planetesimal hypothesis is built on this conception, and 

 postulates the close approach of some massive body to our 

 ancestral sun as the source of dispersion of a possible older 

 planetary system, and the generation of the nebulous orbital 

 conditions out of which our present system grew. However 

 this may be, it must be conceded that in collision and close 

 approach lie possibilities, if not probabilities, of ultimate 

 disaster to the solar system and to our earth. But here, as 

 before, the vital question lies in the time element. How 

 imminent is this liability? The distances between stars 

 are so enormous that, though they move diversely, the con- 

 tingencies of collision or disastrous approach are remote. 

 Nothing but rough computations based on assumptions can 

 be made, but these make disaster to a given sun or system 

 fall, on the average, only once in billions of years. There 

 is no star the nearness of which to us, or the direction of 

 motion of which is such as to threaten the earth at any 

 specific period in the future. There is only the general 

 theoretical possibility or probability. While, therefore, 

 there is to be, with little doubt, an end to the earth as a 

 I>lanet, and while, perhaps, previous to that end conditions 

 inhospitable to life may be reached, the forecast of these 

 contingencies places the event in the indeterminate future. 

 The geologic analogies give fair grounds for anticipating 

 conditions congenial to life for millions or tens of millions 

 of years to come, not to urge the even larger possibilities. 

 But congeniality of conditions does not ensure actual 



NO. 2106, VOL. 83] 



realisation. There arise at once questions of biological 

 adaptation, of vital tenacity, and of purposeful action. 

 Appeal to the record of the animal races reveals in some 

 cases a marvellous endurance, in others the briefest of 

 records, while the majority fell between the extremes. 

 Many families persisted for millions of years. A long 

 career for man may not, therefore, be denied on historical 

 grounds, neither can it be assured ; it is an individual race 

 problem ; it is a special case f the problem of the races in 

 the largest sense of the phrase. 



But into the problem of human endurance two new 

 factors have entered, the power of definite moral purpose 

 and the resources of research. No previous race has shown 

 clear evidence that it was guided by moral purpose in 

 seeking distant ends. In man such moral purpose has 

 risen to distinctness. As it grows, beyond question it will 

 count in the perpetuity of the race. No doubt it will come 

 to weigh more and more as the resources of destructive 

 pleasure, on the one hand, and of altruistic rectitude, on 

 the other, are increased by human ingenuity. It will 

 become more critical as the growing multiplicity of the race 

 brings upon it, in increasing stress, the distinctive 

 humanistic phases of the struggle for existence now dimly 

 foreshadowed. It will, beyond question, be more fully 

 realised as the survival of the fittest shall render its 

 verdict on what is good and what is evil in this realm of 

 the moral world. 



But, to be most efficient, moral purpose needs to be 

 conjoined with the highest intelligence, and herein lies the 

 function of research. None of the earlier races made 

 systematic inquiry into the conditions of life, and sought 

 thereby to extend their careers. W'hat can research do for 

 the extension of the career of man? We are witnesses of 

 what it is beginning to do in rendering the forces of nature 

 subservient to man's control and in giving him command 

 over the maladies of which he has long been the victim. 

 Can it master the secrets of vital endurance, the mysteries 

 of heredity, and all the fundamental physiological processes 

 that condition the longevity of the race? The answer must 

 be left to the future, but I take no risk in affirming that 

 when ethics and research join hands in a broad and earnest 

 endeavour to compass the highest development and the 

 greatest longevity of the race, the era of humanity wilt 

 really have begun. 



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