Page:Popular Astronomy - Airy - 1881.djvu/80

66 of latitude passing through Greenwich was easily computed. Then we have to examine whether this circumference corresponds to the circumference calculated on the supposition that the earth is a spheroid, with a shorter axis of 41,707,600 feet, and a larger axis of 41,847,400 feet, and it is found to correspond well.

By means, then, of meridional measures by triangulation, and the Zenith Sector, and by means of east and west measures by triangulation, and observations with the transit instruments and comparisons of clocks, we have got sufficient information upon the form of the earth. Now, observe the very important conclusion to which that leads. In the observations given in the former lecture, we found that the whole of the heavens appeared to revolve, and we say, either the heavens revolve in the direction from the east, through south, to west; or the earth revolves in the direction from west, through south, to east. Which of these is the more likely? Astronomers agree without exception, that it is the earth which revolves. And I will tell you why. I dare say every person whom I see here has been brought up in the belief that the earth does turn round. But, I ask, if they had not been brought up in that belief, whether they would believe it now from what I am telling them? I do not think they would. Amongst all the subjects of natural philosophy presented to the human mind, there is none that staggers it so effectually as the assertion that the earth moves. We must not be uncharitable, then, towards people in the middle ages who did not believe it. To think that the solid earth moves, that the solid ground is going round at the rate of one thousand miles an hour, do you believe it? I will endeavour to give you grounds for the belief.

In the first place, I must say that even the