Published online by Cambridge University Press: 14 August 2015
The first part of the paper reviews the present state of knowledge of the characteristics of cosmic dust in interplanetary space. Since this is derived from a variety of observational techniques, some attempt is made critically to assess the difficulties in interpretation, particularly those due to differences in observational selection. Attention is drawn to the doubts that recently have arisen concerning the existence of a terrestrial dust cloud. The second part describes some radio investigations of the structure of meteor streams and of the sporadic background. Systematic variations in magnitude distribution with solar longitude which are observed in both the Geminids and Perseids cannot be simply interpreted as due to selective perturbation of the smaller meteoroids. Experimental data are described which point to the existence of considerable radiant structure in the sporadic background.