SVANTE AREHENIUS WALKER 731 



be absorbed by the fluid magma under the great pressures existing. 

 But by extrapolation from known data it may be shown that, al- 

 though at room temperature water is a much weaker acid than silicic 

 acid, yet at high temperatures the reverse is the case, water at 1,000° 

 being probably 80 times .stronger than silicic acid. In the magma, 

 then, water will attack and decompose silicates, and thus be poten- 

 tially stored up in the form of acid and base. When the magma on 

 rising is cooled, the reverse process takes place; water is liberated 

 and at a certain height will overcome the pressure of the column 

 above it, eject the superincumbent fluid, and cause a volcanic erup- 

 tion. A volcano thus acts in much the same way a,s a geyser. The 

 theory aims at explaining the proximate cause of eruptions, and has 

 met with wide acceptance. 



In 1898 Arrhenius wrote a remarkable paper on the action of cos- 

 mic influences on physiological processes, and in 1903 he surprised his 

 chemical friends by publishing his " Lehrbuch der kosmi,schen 

 Physik," a work of extraordinary learning and scholarship. In it 

 he passes under review an extensive collection of observational ma- 

 terial and deals with it according to his own methods. The most 

 striking novelty of treatment is the use he makes of radiation pres- 

 sure, the existence of which had been predicted by Clerk Maxwell. 

 It was applied by Arrhenius to various cosmic phenomena even be- 

 fore its experimental confirmation in the laboratory by Nichols and 

 Hull and by Lebedev. Arrhenius calculated that at the surface of 

 the sun the repulsive force of the radiation would balance the sun's 

 gravitational attraction on black particles of diameter about l.S^u,, and 

 specific gravity 1, and that smaller particles than these would be 

 repelled. Schwarzschild made some necessary corrections and 

 showed that the maximum repulsion would be for completely reflect- 

 ing particles (sp. gr. 1) if their diameter was about 0.16/x, and it 

 would then be 10 times the gravitational attraction. From the sun 

 then we might expect streams of such minute particles to be shot 

 out in all directions. Many of these particles would be electrically 

 charged from the ionisation existing in the sun's gaseous atmosphere. 

 Arrhenius shows how the phenomena of the solar corona, comets, the 

 aurora, and the zodiacal light may be caused or influenced by these 

 particles. 



With the beginning of the present century Arrhenius's thoughts 

 took a new turn. Thorvald Madsen had succeeded in arousing his 

 interest in the application of physico-chemical ideas to serum 

 therapy. In 1900 and 1901 he did some experimental work with 

 Madsen in Copenhagen, and later in Ehrlich's laboratory in Frank- 

 fort. In 1902 he published jointly with Madsen a memoir on the 

 occasion of the opening of the Danish State Scrum Institute, of 

 which Madsen had been appointed director. It was entitled " Physi- 



