THE UNITY OF PHYSICAL SCIENCE 11 



geologists for the different shells of the earth, let us glance rapidly in 

 turn at the sciences of the atmosphere, the hydrosphere or oceans, 

 the lithosphere or crust, and the centrosphere or nucleus. 



The atmosphere is the special province of meteorologists, and 

 although they are not yet able to issue long-range predictions, like 

 those guaranteed by our theories of tides and terrestrial magnetism, 

 it must be admitted that they have made great progress towards 

 a rational description of the apparently erratic phenomena of the 

 weather. One of the peculiar anomalies of this science illustrates 

 in a striking way the general need of additional knowledge of the 

 properties of matter; in this case, especially, the properties of gases. 

 It is the fact that in meteorology greater progress has been made, 

 up to date, in the interpretation of the kinetic than in the inter- 

 pretation of the static phenomena of the atmosphere. Considering 

 that static properties are usually much simpler than kinetic proper- 

 ties, it seems strange that we should know much more about cyclones, 

 for example, than we do about the mass and the mass distribution of 

 the atmosphere. In respect to this apparently simple question meteor- 

 ology seems to have made no advance beyond the work of Laplace. 

 There are indications, however, that this, along with many other 

 questions, must await the advent of a new Principia. 



The geodesists, who are the closest allies of the astronomers, may 

 be said to preside over the hydrosphere, since most of their theories 

 as well as most of their observations are referred to the sea level. 

 They have determined the shape and the size of the earth to a sur- 

 prising degree of certainty; but they are now confronted by pro- 

 blems which depend chiefly on the mass and mass distribution of 

 the earth. The exquisite refinement of their observational methods 

 has brought to light a minute wandering in the earth of its axis of 

 rotation, which makes the latitude of any place a variable quantity ; 

 but the interpretation of this phenomenon is again a physical and 

 not a mensurational problem. They have worked improvements 

 also in all kinds of apparatus for refined measurements, as of base- 

 lines, angles, and differences of level; but here, likewise, they appear 

 to approach limits set by the properties of matter. 



The lithosphere was once thought to be the restricted province 

 of geologists, but they now lay claim to the entire earth, from the 

 centre of the centrosphere to the limits of the atmosphere, and they 

 threaten to invade the region of the astronomers on their way toward 

 the outlying domain of cosmogony. Geology illustrates better than 

 any other science, probably, the wide ramifications and the close 

 interrelations of physical phenomena. There is scarcely a process, 

 a product, or a principle in the whole range of physical science, from 

 physics and chemistry up to astronomy and astrophysics, which is 

 not fully illustrated in its uniqueness or in its diversity by actual 



