The Gronmhvork of the Universe, &c. 75 



possibly even wider ai»i)lications in this field are before us. In 

 geology, radioactivity has given us a new method of measuring 

 the duration of the periods of the Earth's history ; and in 

 Astronomy the radioactive phenomena have thrown fresh light 

 upon the problems of stellar and terrestrial heat. Finally, 

 aeronautics has profited with the rest ; for the helium which 

 arises from radioactive materials buried deep in the Earth's crust 

 is now being utilized for filling airships with a light and non- 

 inflammable gas. 



IV.— SOME PROBLEMS OF FOOD AND POWER. 



[The reader is also referred to Di'. A. K. Macbeth, "Catalysis," p. 34, 

 Proceedings of Society, 1919-20 ; and to Professor William Caldwell, 

 "Fixation of Nitrogen " p. 5, Proceedings of Society, 1917-18.] 



Our modern civilization depends for existence upon its 

 supplies of food and power. It is essential that our teeming 

 populations must be fed, while the mere distribution of food- 

 stuffs involves the expenditure of mechanical energy on a vast 

 scale ; for this reason these subjects were selected as suitable for 

 this fourth lecture. 



The question of food is the more important and may be 

 dealt with first. The main task in the future will be the 

 production of a greater yield of foodstuffs to provide for the 

 constantly increasing population. This object may be obtained in 

 two Avays, either by an increased productivity of the soil, or by 

 the manufacture of artificial foodstuflfs by chemical means. 



Our daily food consists of two main groups of materials : 

 carbohydrates and proteins. Sugar, starch, itc, are carbohydrates, 

 while cereals and meat contain large proportions of proteins. 

 The carbohydrates contain only carbon, hydrogen and oxygen ; 

 while the proteins, in addition to these three, have nitrogen also 

 as one of their components. 



