26 POPULAR SCIENCE MONTHLY. 



LIFE IN OTHER WORLDS. 



By F. J. ALLEN, M.A., M.D., Cantab., 



LATE PROFESSOR OF PHYSIOLOGY IN MASON UNIVERSITY COLLEGE, BIRMINGHAM. 



rriHE question 'whether life exists in any other worlds than our own' 

 -^ is one in which very many persons feel an interest, and about 

 which much has been said and written; but if the man of ordinary 

 education has any ideas on the subject, they are generally mistaken ; and 

 even scientists are prone to regard it too exclusively in the light of 

 their particular science, and thus to conceive and propagate fallacies 

 which might be easily avoided. 



Of course no absolute answer to the question can be given until 

 perchance some hitherto undreamt-of means shall be discovered for 

 the observation of distant worlds. We can hardly forward the matter 

 by mere speculation on general grounds, such as the law of probabilities, 

 or the relative position of worlds in the universe. Nevertheless there 

 is one method by which we can at least guard ourselves against errone- 

 ous speculation, and prepare the way for discovery when the oppor- 

 tunity comes; and that method is, to find out the conditions on which 

 terrestrial life depends, and then to search other worlds and find if 

 possible whether they provide similar or parallel conditions. 



Though the ultimate nature of life is as yet unknown to us, its 

 secrets are being gradually unraveled by research; and it becomes 

 more and more apparent that the phenomena of life are but special and 

 intricate developments of physical action. The most prominent and 

 perhaps most fundamental characteristic of life is what may be called 

 the energy traffic, or the function of trading in energy; and the 

 phenomena of assimilation, growth, movement, etc., are the outward 

 and visible signs of this traflfic. Living substance possesses in the 

 highest degree the property of absorbing radiant energy, as heat or 

 light, storing it in a potential form, and subsequently expending it in 

 active forms such as motion, mechanical work, heat and electricity. 



Actions of this kind are not unknown in the inorganic world. For 

 example, the atmosphere and ocean absorb the energy of light and 

 heat from the sun, store it temporarily and convert it subsequently into 

 the energy of wind and wave, lightning and thunder. But in living 

 substance there exists a more finely coordinated energy-trading system, 

 evolved out of the chemical capacities of a small number of elements 

 acting under the physical conditions which prevail on our planet. 



The energy traffic depends, no doubt, on causes at present unknown 

 to us; and some biologists are wont to personify these causes as a 



