226 FROM NEBULA TO NEBULA 



where all the radiation from the hot celestial bodies is stored up, 

 and where, owing to the enormous distances, the restraining force 

 of gravity is exceedingly feeble. Thus the nebulae will lose their 

 most rapid molecules from their outer portions, and they will 

 therefore be cooling in these outer strata. This loss of heat is 

 compensated by the radiation from the stars. If, now, there were 

 only nebulae of one kind in the whole universe, those escaped 

 molecules would finally land on some other nebula, heat equilib- 

 rium would thus be established between the different nebulae, and 

 the "heat-death" be realized. But we have already remarked 

 that the nebulae enclose many immigrated celestial bodies, which 

 are able to condense the gases from their neighborhood, and which 

 thereby assume a higher temperature. 



The third aim of Doctor Arrhenius is to account for 

 the sun's heat. To this end he prepares the ground by 

 exposing the shortcomings of Helmholtz's hypothesis, as 

 well as of others, and then selects for his own the now 

 familiar conception of the atomic dissociation of matter. 

 In this particular field he is esteemed preeminent, having 

 won the Nobel prize in 1903 for his researches along this 

 line. To quote again from his book (p. 91) : 



It is quite incorrect to assert that high temperatures must 

 necessarily decompose all chemical compounds into their elements. 

 The mechanical theory of heat teaches us only that at rising tem- 

 peratures products are formed whose formation goes hand in 

 hand with an absorption of heat. Thus, at a high temperature, 

 ozone is formed from oxygen, although ozone is more complex 

 in composition than oxygen, and by this reaction 750 calories are 

 consumed when one gramme of oxygen is transformed into one 

 gramme of ozone. We likewise know that in the electric arc, at 

 a temperature of about 3000, a compound is formed under con- 

 sumption of heat by the oxygen and nitrogen of the atmosphere. 

 A new method for the technical preparation of nitric acid from 

 the nitrogen of the air is based upon this reaction. Again, the 

 well-known compounds, benzene and acetylene, are formed from 

 their elements, carbon and hydrogen, under absorption of heat. 

 All these bodies can only be synthetized from their elementary 

 constituents at high temperatures. We further know from ex- 

 perience that the higher the temperature at which a reaction takes 

 place, the greater, in general, the amount of heat which it absorbs. 



A similar law applies to the influence of pressure. When the 

 pressure is increased, such processes will be favored as will yield 

 products of a smaller volume. If we imagine that a mass of gas 

 rushes down from a higher stratum of the sun into the depths 

 of the sun's interior, as gases do in sun-spots, complex com- 



