44 Correspondence. [January, 
are so small compared with the lunar tides that we have hitherto 
overlooked them. Reasoning mathematically, Prof. Ball con- 
cludes that, before the Moon existed, the Earth was disturbed by 
the solar tides alone. These primitive tides were manifested as 
throbs in the adtual body of the Earth itself, which was then in 
a more or less fluid condition. Though at this remote epoch 
the solar tides were small, as they are at present, a succession of 
impulses can produce a great effect. At first the vibrations were 
small “ but at each succeeding impulse the amplitude was aug- 
mented, until at length the cohesion of the molten matter could 
no longer resist : a separation took place ; one portion consoli- 
dated to form our present Earth ; the other portion consolidated 
to form the Moon.” 
Thus, according to Prof. Ball, the Earth and the Moon were 
created. I have not in my book ventured to enter into such 
minute detail, but I am exceedingly glad to find that the Astro- 
nomer Royal for Ireland does not see any mathematical objection 
to my theory of the Moon’s receding motion. 
The Moon, having thus assumed an independent existence, 
began to recede very slowly from the Earth, and Prof. Ball thinks 
that, at the time when the earliest stratified rocks were being 
laid down, it may have been 40,000 miles away from it. “ On 
the primitive oceans the Moon raised tides as it does at present ; 
but the 40,000-mile Moon was a far more efficient tide-producer 
than our 240,000-mile Moon. The nearer the Moon the greater 
the tide. To express the relation accurately we say that the 
efficiency of the Moon in producing tides varies inversely as the 
cube of the distance. ... If the present tides be 3 feet, and if 
the early tides be 216 times their present amount, then it is plain 
that the ancient tides must have been 648 feet. . . . These 
mighty tides are the gifts which Astronomers have now made to 
the working machinery of the Geologist. They constitute an 
engine of terrific power to aid in the great work of Geology. . . . 
As the Moon recedes, the period which it requires for a journey 
round the Earth increases also. . . . Do not infer that the rate 
of the Earth’s rotation is increasing ; the contrary is the fadt. 
The Earth’s rotation is getting slower, and so is that of the 
Moon;, but the retardation of the Moon is much greater than 
that of the Earth. Even though the rotation of the Earth is 
much more than the primitive three hours, yet that of the Moon 
has increased to several times that of the Earth.” 
Such are the discoveries which Prof. Ball has made by the 
light of mathematical reasoning, whilst sitting, as he says, at 
his desk, and as the result of diligent labours of the most 
abstruse kind. 
The Professor does not, however, inform us by what means 
the Moon has reached its present distance from the Earth. He 
obviously believes that gravitation is an absolute force in Nature, 
and not, as Newton taught, a purely abstract conception of the 
