Astronautics is the scientific study of the many problems which arise when we contemplate the possibility of releasing man from the Earth’s gravitational field, setting him free to explore the Solar System and later the regions beyond. Not so long ago, to admit having such ambitions was regarded as a symptom of megalomania. Mathematical “proofs” of the impossibility of escape from the Earth’s field were legion and ranged from the simple statement “a rocket will not develop thrust in a vacuum” to a (perfectly correct) numerical calculation showing that the most powerful fuel possesses insufficient energy to release even its own mass from the Earth’s attraction. It was made very clear to the early enthusiasts that few advances in this field could be made until the climate of scientific opinion changed and astronautics became “respectable”. It is, of course, quite normal for a line of scientific enquiry to evolve from the stage at which its ideas are the subject of ridicule to the stage at which they are universally acclaimed. The idea of the periodic classification of the elements caused our great-grandfathers to laugh hugely into their beards. Marconi was a notorious striver after the unattainable. The Wright brothers achieved the “impossible” and, in defiance of contemporary opinion, the aeroplane proceeded to change our way of life irrevocably. Astronautics has been singularly fortunate. After spending comparatively few years in the wilderness, the advent of the V.2 and other rocket weapons brought about that change in the attitude of scientists towards the subject which had been seen as a necessary preliminary to the serious consideration of the problems involved. Greatly decimated, the doubters now depend upon the slogan—“it can be done, but it is not worth doing”. However, it is not the purpose of this article to discuss the value, in human terms, of conquering space but only to explain briefly why and how it can be done if man so desires. In any case, it is unlikely that the real significance for mankind of such a tremendous advance can be appreciated before the event. Only the passing of the years can reveal to us the value of our actions.

It is surely a very remarkable thing that despite the range, power and success of modern mathematics, the concept of natural number, on which the whole edifice rests, is still something of a mystery.

Towards the end of the last century the great German mathematician and philosopher Gottlob Frege, dissenting strongly from the view current in his time—and perhaps still today—that number is either a physical or a mental entity, gave the first purely logical definition of a natural number. His work aroused so little interest at the time that his definition remained practically unknown until it was rediscovered by Bertrand Russell 20 years later. The definition, though a little strange at first sight, is quite simple and is based upon a notion which is of first importance in many branches of mathematics, the notion of a (1, 1) correspondence.

When one first comes across the formulae

one is immediately struck by the fact that the second sum is the square of the first. The usual methods of proof give no reason to expect that the sums will be related in such a pleasant and easily memorable way; one is left with the impression that this is a happy accident. The following proof may give some entertainment because it throws light on this point; it emerged unexpectedly out of the tortuous process of making up a question for a recent Scholarship examination.

The rhombic dodecahedron has been described by Hope-Jones, Math. Gazette, Vol. XX, p. 254 (1936); it can be obtained simply by taking a cube, joining each vertex to the centre, thus obtaining six square pyramids, and placing these pyramids on the faces of a second cube. The solid thus constructed is shown in fig. 1.