As the author of the article in NATURE of October 24, 1918, in which the diagram referred to by Dr. Hutchinson last week was first brought to the notice of your readers, may I be permitted to supplement the information as to previous efforts in the same direction? When the diagram first appeared in this country Rear-Admiral Parry, Hydrographer to the Admiralty, also set on foot an inquiry similar to that of Dr. Hutchinson, and very courteously sent me the result of his investigation. From his report it appears that “an account of the ‘Nomogramme’ was published in Petermann's Mittelungen (vol. ii., pp. 182 and 249, 1913), and was illustrated by a skeleton diagram similar in principle to these charts, and the method for using it was fully explained.” This, in point of time, is fifteen years later than the date of the paper of M. d'Ocagne, who, so far as appears at present, is clearly entitled to the credit claimed for him as first in the field.