and recollecting that each foot corresponds to one hundred and eighty-six million miles, we discover the distance of the star.  If the stars were comparatively near us, the process would be a very simple one; but, unfortunately, the stars are so extremely far off that this triangle, even with a base of only one foot, must have its sides many miles long.  Indeed, astronomers will tell you that there is no more delicate or troublesome work in the whole of their science than that of discovering the distance of a star.

In all such measurements we take the distance from the earth to the sun as a conveniently long measuring-rod, whereby to express the results.  The nearest stars are still hundreds of thousands of times as far off as the sun.  Let us ponder for a little on the vastness of these distances.  We shall first express them in miles.  Taking the sun’s distance to be ninety-three million miles, then the distance of the nearest fixed star is about twenty millions of millions of miles—­that is to say, we express this by putting down a 2 first, and then writing thirteen ciphers after it.  It is, no doubt, easy to speak of such figures, but it is a very different matter when we endeavor to imagine the awful magnitude which such a number indicates.  I must try to give some illustrations which will enable you to form a notion of it.  At first I was going to ask you to try and count this number, but when I found it would require at least three hundred thousand years, counting day and night without stopping, before the task was over, it became necessary to adopt some other method.

When on a visit in Lancashire I was once kindly permitted to visit a cotton mill, and I learned that the cotton yarn there produced in a single day would be long enough to wind round this earth twenty-seven times at the equator.  It appears that the total production of cotton yarn each day in all the mills together would be on the average about one hundred and fifty-five million miles.  In fact, if they would only spin about one-fifth more, we could assert that Great Britain produced enough cotton yarn every day to stretch from the earth to the sun and back again!  It is not hard to find from these figures how long it would take for all the mills in Lancashire to produce a piece of yarn long enough to reach from our earth to the nearest of the stars.  If the spinners worked as hard as ever they could for a year, and if all the pieces were then tied together, they would extend to only a small fraction of the distance; nor if they worked for ten years, or for twenty years, would the task be fully accomplished.  Indeed, upwards of four hundred years would be necessary before enough cotton could be grown in America and spun in this country to stretch over a distance so enormous.  All the spinning that has ever yet been done in the world has not formed a long enough thread!

There is another way in which we can form some notion of the immensity of these sidereal distances.  You will recollect that, when we were speaking of Jupiter’s moons, I told you of the beautiful discovery which their eclipses enabled astronomers to make.  It was thus found that light travels at the enormous speed of about one hundred and eighty-five thousand miles per second.  It moves so quickly that within a single second a ray would flash two hundred times from London to Edinburgh and back again.