INITIATORY FORCES. 15^ 



trace thera to a common source. Observations at Kew for a series of 

 years have detected that the proximity of Mercury and Venus to the 

 sun seems to control the size and direction of the solar spots ; and 

 therefore it appears that these planets mediately through the sun cause 

 our auroras and magnetic storms. There is also reason to believe 

 that the production of sun-spots diminishes by absorption the actinic 

 rays, while the thermal ones are not noticeably affected ; for to the 

 actinic rays the chemical or ripening effect is due. Years of minimum 

 sun-spots have been found to coincide very nearly witli the good wine- 

 years in Germany. At first sight we are startled by the supposi- 

 tion that a planet like Venus, which comes nearer to the earth than 

 it ever does to the sun, should in any way be accountable for such 

 enormous manifestations of energy as those which occur over the 

 sun's surface. But the wonder will disappear if we bear in mind that 

 there may be two kinds of causes or antecedents. Thus, we say that 

 the blacksmith is the cause of the blow which his hammer strikes the 

 anvil, and here the strength of the blow depends upon the strength 

 of the smith. But we may likewise say that the man who pulls the 

 trigger of a gun or cannon is the cause of the motion of the ball, and 

 here there is no relation between the strength of the effect and that 

 of its cause. Now, in whatever mysterious way Venus and Mercury 

 affect the sun, we may be sure it is not after the fashion of the black- 

 smith : they do not deal him a violent blow producing all this enor- 

 mous effect, but they rather pull the trigger, and immediately a very 

 great change takes place. And, in passing, we are here taught how 

 involved the relations of the parts of the universe may be. Two 

 planets whose direct influence on the earth by their gravitation and 

 light is quite inconsiderable, yet, by their indirect effects through their 

 action on the sun, produce very marked and varied results on the sur- 

 face of our globe. Many laboratory experiments, on a small scale, 

 illustrate the potency of initiatory forces. A pail of water, main- 

 tained in great stillness, may be gradually chilled several degrees be- 

 low the common freezing-point, when the formation of a cake of ice 

 instantly follows from a slight shake. A clean glass vessel may be 

 filled with water and slowly brought to a temperature in excess of 

 the ordinary boiling-point, and a feeble shock is all that is needed for 

 the prompt liberation of a large volume of steam. Crystallization 

 offers similar results. A supersaturated solution of a salt may long 

 remain in the liquid state until a crystalline fragment thrown in in- 

 stantly serves as a nucleus for extensive solidification. When such a 

 solution contains two salts, which begin to crystallize about the same 

 temperature, when a solid fragment of each kind is thrown into the 

 liquid, it picks out its kindred without the slightest error, and grows 

 thereby. A new surgical method for covering a wound with skin em- 

 ploys as centres of growth tiny morsels of skin supplied from else- 

 where. These gather together elements akin to themselves, and soon 



