With increasing distance, our knowledge fades, and fades rapidly. Eventually, we reach the dim boundary-the utmost limits of our telescopes. There, we measure shadows, and we search among ghostly errors of measurement for landmarks that are scarcely more substantial. The search will continue. Not until the empirical resources are exhausted, need we pass on to the dreamy realms of speculation.

At the last dim horizon, we search among ghostly errors of observations for landmarks that are scarcely more substantial. The search will continue. The urge is older than history. It is not satisfied and it will not be oppressed.

The great spirals, with their enormous radial velocities and insensible proper motions, apparently lie outside our Solar system.

The outstanding feature, however, is the possibility that the velocity-distance relation may represent the de Sitter effect, and hence that numerical data may be introduced into discussions of the general curvature of space.

Not until the empirical resources are exhausted, need we pass on to the dreamy realms of speculation.

With increasing distance, our knowledge fades, and fades rapidly. Eventually, we reach the dim boundary-the utmost limits of our telescopes. There, we measure shadows, and we search among ghostly errors of measurement for landmarks that are scarcely more substantial. The search will continue. Not until the empirical resources are exhausted, need we pass on to the dreamy realms of speculation.

The history of astronomy is a history of receding horizons.