High-resolution Ha filtergrams, made with a -81-angstrom birefringent filter, are described. A detailed study is made of the dark, fine mottles which are visible in the line wings. At low solar latitudes these dark, fine mottles have the following properties: (a) They are frequently elongated; the average length is 4'S, and the width lies between 0"7 and 1'S. (b) The average lifetime is 15.5 minutes. During the first half of their lifetime, however, they are best visible only in the violent Ha wing and during the second hall in the red wing. (c) From orientations near the solar limb they are shown to be predominantly vertical to the solar surface. (d) The total number of these mottles on the sun is found to be 4 X 1 . (e) From the spectrum, the Doppler width is found as 0.50 A, the optical depth is of the order of 5, and the source function is about 3 X 1013 erg . Mi these properties appear to agree with those expected of spicules in projection on the solar disk. There is little doubt that the mottles actually are spicules.
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J. M. Beckers (1963) studied this question.