Earth is the cradle of humanity, but one cannot remain in the cradle forever.

The Earth is the cradle of humanity, but mankind cannot stay in the cradle forever.

Mankind will not forever remain on Earth but, in the pursuit of light and space, will first timidly emerge from the bounds of the atmosphere and then advance until he has conquered the whole of circumsolar space.

Man must at all costs overcome the Earth's gravity and have, in reserve, the space at least of the Solar System.

Men are weak now, and yet they transform the Earth's surface. In millions of years, their might will increase to the extent that they will change the surface of the Earth, its oceans, the atmosphere, and themselves.

My entire life consisted of musings, calculations, practical works, and trials. Many questions remain unanswered; many works are incomplete or unpublished. The most important things still lie ahead.