Mysteries of Time and Space (Paperback)

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: THE BIRTH OF THE MOON. Fourteen years have passed since, in the first series of my ' Light Science for Leisure Hours,' I discussed the change which the tidal wave is slowly but surely producing in the length of the day. Certain researches, which had then recently been made into the moon's motions, had shown astronomers that there must be some force at work retarding the earth in her rotational spin. 'In this difficulty,' I wrote at that time, ' we are not left wholly without resource.' We are not only able, I showed, to say that the discrepancy between the moon's motions and theory is due to a gradual retardation of the earth's rotation-movement, but we are able to place our finger on a very sufficient cause for such a retardation. One of the most firmly established principles of modern science is this, that where work is done, force is in some way or other expended. The doing of work may show itself in a variety of ways?in the generation of heat, in the production of light, in the raising of weights, and so on; but in every case an equivalent force must be expended. If the brakes are applied to a train in motion, intense heat is generated in the substance of the brake. Now, the force employed by the brakesman is not equivalent to the heat generated. Where then is the balance of force expended ? We all know that the train's motion is retarded, and this loss of motion represents the requisite expenditure of force. ' Now,' I asked, ' is there any process in nature resembling, in however remote a degree, the application of a brake to check the earth's rotation ?' ' There is,'was the answer ; ' the tidal wave, which sweeps twice a day round the earth, travels in a direction contrary to the earth's motion of rotation. That this wave " does work" no one can doubt who has watched its ...