I 885 .J 
The Heat of the Sun. I3I 
3 !?r,V f , the Earth w , ere t0 faI1 int0 the Sun the heat which 
ou d be given out by the sudden stoppage of the motion 
would be sufficient to keep up the present rate o?°o“ar 
emission for a period of 94 years 303 days. In addition to 
the amounts given in the Table there must be added the heat 
tt'lneT “ t e s P1 ° dUC \ d - b ? the stoppage of the rotation of 
e planet on its axis, which in the case of the Earth would 
supply the Sun for 81 days. “ The heat of rotation of the 
Sun and planets, taken together, would cover the solar 
f/haf S1 ° n a 01 ' r ^, yea ;; S ’ Whlle the total heat of gravitation 
(that pioduced by the planets falling into the Sun) would 
cover dhe emission for 45,589 years.”— (Tyndall.) 
In the foregomg sketch of a theory which has influenced 
so mightily the progress of solar physics, I have endeavoured 
to confine myself as much as possible to the words of its 
authors and supporters. In taking a survey of it in its 
entirety we cannot but be struck by the really beautiful way 
in which everything is derived from one original and all- 
pervading law— that of gravitation. 
Given the existence of matter and the law of gravitation 
the theory shows how the universe may have been produced’ 
I he same force which causes the apple to fall to the ground 
acting through distant ages, gave us the light and heat of 
the Sun which caused the apple to ascend on the tree 
Unity and design pervades the whole, and this is what we 
find eveiy where in Nature. 
Again, throughout the whole of the theory there is no 
assumption of either hypothetical substances or hypothetical 
forces; no luminiferous ether with its Protean properties, 
the single blot on the Undulatory Theory of Light • no 
attractive and repulsive zones, as in the Corpuscular Theory 
Starting with matter as we find it on the Earth, it works 
out its results according to the operations of known and 
oroughly established laws. This is an important point 
t i? e i° ry i WaS pro P ounded and worked out long before 
Knchhoff had given to the world his immortal discovery of 
the existence of terrestrial matter in the Sun. Subsequent 
discovery proves that the universe contains no matter not 
o?her ng ° n the Eaith ’ and thC Meteoric The ory calls for no 
What I may call the essential elements of a theory are 
therefore here present; its ultimate fate must therefore de- 
pend upon some more probable explanation being proposed 
^ e rightly consider the prediction of a hitherto unknown 
phenomenon, which is afterwards proved to be true as a 
triumph of theory. Thus the discovery of Neptune and 
