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

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.

All nature is a vast symbolism: Every material fact has sheathed within it a spiritual truth.

Wisdom cannot be directly transmitted, and does not readily accumulate through the ages.

Equipped with our five senses - along with telescopes and microscopes and mass spectrometers and seismographs and magnetometers and particle accelerators and detectors sensitive to the entire electromagnetic spectrum - we explore the universe around us and call the adventure science.

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

The great spirals... apparently lie outside our stellar system.