284 THE POPULAR SCIENCE MONTHLY. 



equation. Now, that point is given definitely as a point of time, not 

 with great accuracy, but still as near as we can expect to get it, with 

 such means of measuring as we have, and Sir William Thompson has 

 calculated that the earth must have solidified at some time a hundred 

 millions or two hundred millions of years ago ; and there w^e arrive 

 by a present state of things at the beginning of the process of cool- 

 ing the earth which is going on now. Before that it was cooling as a 

 liquid, and in passing from the liquid to the solid state there was a 

 catastrophe which introduced a new rate of cooling, so that by means 

 of that law we do come to a time when the earth began to assume the 

 present state of things not that of the existence of the universe at 

 all; we do not give the time of the commencement of the universe, 

 but simply the structure of the earth. If we went farther back, we 

 niio;ht make a further calculation and find how Ions the earth had 

 been in a liquid state. We should come to another catastrophe, and 

 say at that time, not that the universe began to exist, but that the 

 present earth passed from the gaseous to the liquid state. And if we 

 went farther back still we should probably find the earth falling 

 together out of a great ring of matter surrounding the sun, and dis- 

 tributed over its orbit. The same thing is true of every body of 

 matter: if we trace its history back, we come to a certain time at 

 which the catastrophe took place, and if we were to trace back the 

 history of all the bodies of the universe in that way we should con- 

 tinually see them separating up, and falling together, as they have 

 done. What they have actually done is to fall together and get solid. 

 If we should reverse the process we should see them separating and 

 getting cool, and, as a limit to that, we should find that all these bodies 

 would be resolved into molecules, and all these would be flying away 

 from each other. There would be no limit to that process, and we 

 could trace it as far back as ever we liked to trace it. So that on the 

 assumption, a very large assumption, that the present constitution of 

 the laws of geometry and mechanics has held good during the whole 

 of past times, we should be led to the conclusion that at an inconceiv- 

 ably long time ago the universe did consist of ultimate molecules, all 

 separate from one another, and approaching one another, because we 

 have to revei'se our former process. Instead of their being at a great 

 distance from one another, and all traveling toward some place where 

 they would meet, the reverse would be the case. Then you would 

 have the process of chlorine going on in these bodies, exactly as we 

 find it going on now, but you will observe that we do not come to 

 such a catastrophe as implies that we have to stop these laws of Na- 

 ture, We come to something of which we cannot make any further 

 calculation ; we find that, however far we like to go back, we approx- 

 imate to that actual state of things, but never actually get to it. 

 Here we have a doctrine about the beginning of things. First, we 

 have a probability, aboirt as correct as science can make it, of the 



