When the diameter of a molecule has been measured, as it has been approximately, and found to be about one fifty-millionth of an inch, then fifty million in a row would reach an inch, and the cube of fifty million is 125,000,000000,000000,000000, one hundred and twenty-five thousand million million millions. In a cubic foot there will of course be 1728 times that number. One may if one likes find how many there may be in the earth, and moon, sun and planets, for the dimensions of them are all very well known. Only the multiplication table need be used, and the sum of all these will give how many molecules there are in the solar system. If one should feel that the number thus obtained was not very accurate, he might reflect that if there were ten times as many it would add but another cipher to a long line of similar ones and would not materially modify it. The point is that there is a definite, computable number. If one will then add to these the number of molecules in the more distant stars and nebulæ, of which there are visible about 100,000,000, making such estimate of their individual size as he thinks prudent, the sum of all will give the number of molecules in the visible universe. The number is not so large but it can be written down in a minute or two. Those who have been to the pains to do the sum say it may be represented by seven followed by ninety-one ciphers. One could easily compute how many molecules so large a space would contain if it were full and as closely packed as they are in a drop of water, but there would be a finite and not an infinite number, and therefore there is a limited number of atoms in the visible universe. THE ETHER IS UNLIMITED.