Interplanetary Dust Distribution.

A detailed calculation of the dust-scattered light at very small elongations from the sun (2-10 solar radii) reveals (1) that the dust is distributed as r , where r is the distance from the sun and " is some number possibly less than, but most probably equal to, 1.5; (2) that the minimum radius of the dust particles is a few microns; (3) that the particle concentration depends on the particle radius, a, as a- , where p is a number possibly equal to, but most probably greater than, 2.5; (4) that the scattered light should depend linearly on the square root of the wave length of the light; (5) that the concentration of dust at the earth's orbit is, to a good approximation, 10-' -10-' particle/cc; but (6) that, because of the earth's gravitational field, the concentration at the earth's surface may be increased to as much as 10- -11 particle/cc. A less precise calculation of the zodiacal light observed at large elongations from the sun (greater than 30 ) favors the upper limit to for the radial distribution of the coronal calculation and confirms the absolute value of the concentration inferred from the solar corona if the dust albedo is assumed to be approximately 0.1.