Spirals in Nature and Art

I HAVE to thank you for a very kind notice of my little essay on spirals, and I venture to trouble you further on the subject, because your last paragraph, criticising my attribution of spiral curves in flight to Leonardo, gives me an opportunity of making a correction to which, I feel sure, your courtesy to a distinguished scientific writer will enable me to give publicity. It appears that, in pp. 153 to 155 of my study of spirals, and in the figures 45 and 46 therein included, I have unconsciously done an injustice to the original researches on flight published by Dr. J. Bell Pettigrew, M.D., LL.D., F.R.S., Chandos professor of medicine and anatomy at the University of St. Andrew's, who, I now find, has been steadily engaged on the problem of flight since 1867, and has apparently published many papers and memoirs on the subject in the Proceedings of the Royal Institution of Great Britain, the Transactions of the Linnean Society and of the Royal Society of Edinburgh, and elsewhere.