288 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1963 



indeed be a calamity, but oddly enough tliere seems to be no well 

 attested case of anyone being killed by a meteorite fall. Some years 

 ago a person in America was injured by a meteorite but even this 

 was from the first bomice of a small fragment. There has been some 

 discussion about the dangers of these meteors and meteorites to space 

 travelers, but the chances of being hit by anything which could do 

 serious damage to a space ship is so small that none of the experts 

 really worry about it. Of course the astronauts who land on the 

 moon will need protection, because there is no atmosphere to act as 

 a shield even from the micrometeorites. 



The refinement of the measurements made in space probes and 

 satellites, coupled with further development in the ground-based 

 photographic and radio-echo meteor work, will certainly lead to a 

 much better understanding of the role of these particles in the 

 formation and evolution of the solar system. At present it is believed 

 that the large meteorites which fall to earth have a different origin 

 from the meteors. Are the meteorites an extension of the size range 

 of meteors, or are they a separate class ? Does all this debris represent 

 samples of the primeval material left over from the fonnation 

 of the solar system or is it the consequence of some subsequent 

 planetary catastrophe? It is clear that an extraordinarily complex 

 situation exists in the solar system in the space between the earth 

 and planets and the sun, not only of electromagnetic radiation but 

 of corpuscular radiation, and of solid material particles in the form 

 of dust and pieces of stone and iron. 



THE MOON AND THE PLANETS 



The techniques of radio astronomy and the space probe seem to be 

 on the verge of increasing markedly our knowledge of the moon and 

 the planets. For example, in the case of the moon, the radio astro- 

 nomical work has already given some extremely interesting results. 

 Ten years ago it was a difficult teclmological problem to transmit 

 radio waves from earth and pick them up again 2i/^ seconds later 

 after they had been reflected from the surface of the moon nearly 

 a quarter of a million miles distant. Now^, with the large radio 

 telescopes, this is an easy technical task but, as so often happens with 

 new scientific experiments, completely unexpected effects were en- 

 countered. The moon appears to be fairly uniformly bright to the 

 eye, and it was assumed that if radio waves of uniform strength were 

 transmitted to the moon, then they would be scattered uniformly 

 from the lunar surface so that the signals collected by the radio 

 telescope and recorded as echoes on a cathode ray tube would always 

 be of the same strength. It was surprising to find that this was not 

 the situation. The transmissions from the telescope were made in the 

 form of short pulses which were expected to be recorded as pulses 



