We can only hope the next cycle will see the following-up of the question and its final solution; more astrophysicists are devoting themselves to the problems of Mars, and if their researches do not bring us the complete solution of the 'Martian problem', they will at least enable us to make definite progress; and we can thus reasonably hope that at the end of the next cycle, in 1956, the present book will appear very much out of date!