4 METEOROLOGY 



the sun, ending with the conclusion that the minimum temperature on the earth occurs 0.65 

 year after the maximum of sunspots, whereas our maximum temperature occurs 0.33 year 

 before the minimum of sunspots. He infers that there may be fluctuations of plus or minus 

 two-tenths of one per cent in the earth's temperature, but whether this terrestrial phenomenon 

 is due to variations of solar radiation or of atmospheric conditions is still problematical, 



The Solar Commission under the presidency of Sir Norman Lockyer continues its ener- 

 getic labours, bearing on variations in the physical relations of the sun and the earth. Such 

 variations are delicate and obscure and apt to be deceptive; it is not as yet clear that any 

 variations in the solar conditions exist whose effects are appreciable in comparison with the 

 variations continually going on in our own atmosphere. Koeppen showed that the so-called 

 sunspot period in local temperature records varied with the latitudes of our stations, and 

 was essentially a transfer from the equator towards the pole of waves of heat that may have 

 had their origin in our own atmosphere; the obscuration of our upper atmosphere produced 

 by the eruption of Krakatoa spread slowly for a number of years; analogous effects were 

 produced by Skaptas Jokul in 1783; and the eruptions of 1912 in Alaska cut off appreciable 

 amounts of insolation; similarly the short periods that have been worked out by W, J. S. 

 Lockyer may have a terrestrial origin. The broader study of our atmosphere as a whole has 

 been especially favoured by the great increase in the area of the daily weather maps now 

 published in Europe, Asia, Australia and America, and still more light will be thrown on the 

 subject when a daily map of Southern Africa is published by the South African Union. 



(CLEVELAND ABBE.) . 

 PHYSICAL SCIENCE 1 



While failing to chronicle any experimental discoveries of the first importance, the 

 last few years have witnessed a tendency towards certain very radical changes in general 

 physical theory. In their extreme form, these changes amount to a new definition of 

 our units of space and time, the suppression of the interstellar aether as a physical 

 reality, and the conception of a discrete or corpuscular structure of energy. None of 

 these new principles has as yet been fully recognised, but the rapidly increasing number 

 of their adherents renders it necessary to take them seriously into account. 



The Principle of Relativity. The uniform failure of all attempts to discover " abso- 

 lute " motion through the aether, even under the promising conditions of the classical 

 experiment of Michelson and Morley, 2 was met in the first instance by FitzGerald and 

 Lorentz's hypothesis of a shrinkage of all matter in the direction of such motion. 

 Such an hypothesis, though not unreasonable, was entirely arbitrary, and open to the 

 objection that the amount of shrinkage should depend in some way upon the substance 

 in question. 



A more radical solution was furnished in 1905 by Dr. Albert Einstein, of Bern, now 

 Professor of Theoretical Physics in the German University of Prague. This solution 

 is based on the " Principle of Relativity," a principle which extends to electromagnetic 

 phenomena that independence of absolute motion which has been accepted for mechan- 

 ical systems since the days of Newton. It makes two fundamental assumptions, which 

 may be put concisely as follows: (i) It is impossible to discover absolute motion by 

 means of electromagnetic (including optical) phenomena; (2) the velocity of light is a 

 universal constant, independent of the motion of the source. 3 



Since this principle was put forward, a system of theoretical physics has been 

 worked out in considerable detail on the new basis. This system is known as the 

 Theory of Relativity. Among its chief exponents may be mentioned Minkowski, 

 Laue, Herglotz, Noether, Tolman, Born, Frank, N. Campbell and Levi-Civita. The 

 theory, though starting with a renunciation, leads to some very startling positive 

 assertions. It involves a new definition of time, based upon the impossibility of syn- 

 chronising two distant clocks by means of anything more rapid than light-signals. 

 This limitation introduces the velocity of light as a disturbing factor in the synchronism 

 of a clock " at rest " with a clock in (relative) motion. In fact, two clocks, originally 



(v\ 

 -J 2 sec. per 



second, if we denote their relative velocity by v and the velocity of light by c. A rigid 

 sphere in motion, viewed from a system " at rest," appears flattened in the ratio of 



1 See generally E. B. articles on "Physics" enumerated in Index Volume, p. 940. 



2 Philosophical Magazine, 24, p. 449 (1887). 3 Annalen der Physik, 17, pp. 891 (1905). 



