In fr. 69 Smith, the Epicurean Diogenes of Oinoanda, like Lucretius 4.353–63, explains why a square tower viewed from the distance appears to be round. The explanation is that εἲδωλα, filmy atomic images, emanating from the tower, are forced out of shape by the air through which they pass on their way to our eyes. Diogenes’ account is fragmentarily preserved on a stone which I discovered in 1970. The stone bears the right half of one fourteen-line column and the left half of a second one. I first published the text in 1971. When, twenty years later, I came to deal with it again, in preparing an edition of all the known fragments, I was able, thanks in no small measure to the discussions and suggestions of other scholars, whose names can be seen in my apparatus criticus, to print a text which represents a considerable advance on that of the editio princeps. However, with so much of what Diogenes wrote missing, there has remained scope for further progress, and in this note I correct an error—an error present not only in my text, but also on the stone itself.