is 230 feet. We have got back to the length of those long thin telescopes which were found so inconvenient two hundred years ago; but now they are no longer inconvenient because they need not be moved about, but can be fixed upright once for all.

The High "Tower" Telescope on Mount Wilson. That is of course not altogether an easy matter, because a telescope must be fixed very steadily; it will not do, for instance, for it to be shaken by the wind. How are we to prevent a tower 150 feet high from being shaken by the wind? Professor Hale thought of a trick as neat and simple