THE PRESIDENTS ADDRESS. 359 



are indestructible, and only their form can be changed ; while 

 life, as we all know, can be completely destroyed, without passing 

 into any other condition from which it can be resuscitated in its 

 ordinary form. 



Arrhenius believes that the life which populates our globe came 

 to it from other inhabited worlds, the means of transport being the 

 so-called radiation-pressure. It has been established by physicists 

 that minute particles of matter below a certain size can be 

 propelled through infinite space by the pressure of rays of light, 

 heat, and all kinds of radiations, and could travel in this way 

 from planet to planet or from star to star. In this way living^ 

 organisms of a certain degree of minuteness could be disseminated 

 all over the universe and could settle wherever the conditions 

 were favourable. Intensely heated, incandescent bodies giving 

 out powerful radiations, such as the sun for example, would 

 repel them long before they came near enough to be damaged, 

 but on relatively cold planets or heavenly bodies on which the 

 conditions are such that life is able to exist, they could be the 

 starting-point of an evolution of life such as that which has 

 taken place on our globe, an evolution similar as regards its 

 starting-point but not necessarily so as regards its products. 

 This is the so-called doctrine of panspermia, according to which 

 life exists throughout the whole universe in the form of minute 

 germs, capable of further development wherever circumstances 

 permit. 



The germs themselves, when floating freely in the inter- 

 planetary space, would be subjected to a temperature of about 

 220 C, a temperature at which all chemical reactions are 

 arrested ; they would therefore be in a dormant state, in which 

 all vitality was suspended. They could not therefore undergo 

 any process of multiplication in the interstellar space, and if 

 their numbers were not recruited in some way, the stock of 

 germs floating freely in space would diminish continually and 

 would be absorbed and locked up in those heavenly bodies on 

 which the particles could settle. It is therefore necessary to 

 suppose that the germs can be wafted away from worlds on 

 which they have settled and that other worlds besides ours are 

 inhabited by living things. So far as our solar system is con- 

 cerned, Arrhenius believes that Venus and Mars probably 

 harbour life, but that Jupiter, Saturn, Uranus, and Neptune 



