two
o'clock
`` Here is the start of the thing , '' he said . `` There are two hundred and fifty of these reflectors arranged in a circle four hundred yards in diameter . Each of them is an opened parabola of such spread that their beams will cover an area ten yards in diameter at fifty miles above the earth . If my calculations are correct they should penetrate through the layer at an average speed of fifteen miles per hour per unit , and by two o'clock to-morrow afternoon , the road to space should be open . '' `` What is your power ? '' I asked . `` Nothing but a concentration of infra-red rays .