36 INDUCTION. 



it is no longer by the addition of equal quantities in 

 equal times ; the quantities added are unequal, and 

 even the quality may now be different. If the change 

 in the state of the permanent cause be progressive, the 

 effect will go through a double series of changes, 

 arising partly from the accumulated action of the 

 cause, and partly from the changes in its action. The 

 effect is still a progressive effect, produced, however, 

 not by the mere continuance of a cause, but by its 

 continuance and its progressiveness combined. 



A familiar example is afforded by the increase of 

 the temperature as summer advances, that is, as the 

 sun draws nearer to a vertical position, and remains a 

 greater number of hours above the horizon. This 

 instance exemplifies in a very interesting manner the 

 twofold operation on the effect, arising from the con- 

 tinuance of the cause and from its progressive change. 

 When once the sun has come near enough to the 

 zenith, and remains above the horizon long enough, 

 to give more warmth during one diurnal rotation than 

 the counteracting cause, the earth's radiation, can 

 carry off, the mere continuance of the cause would 

 progressively increase the effect, even if the sun came 

 no nearer and the days grew no longer ; but in addi- 

 tion to this, a change takes place in the accidents of 

 the cause (its series of diurnal positions), tending to 

 increase the quantity of the effect. When the summer 

 solstice has passed, the progressive change in the 

 cause begins to take place the reverse way; but, for 

 some time, the accumulating effect of the mere 

 continuance of the cause exceeds the effect of the 

 changes in it, and the temperature continues to 

 increase. 



Again, the motions of a planet are a progressive 

 effect, produced by causes at once permanent and pro- 



