May I be permitted to make some comments on the interesting paper by Dr. Robb in the July number of the Gazette? The point he raises is indeed interesting; though, without his having said so, I should have been surprised to find that it was not generally known; that the Time-Space Theory may, in a limiting instance, be incompatible with Euclid’s (I, 4). My comments must in a sense be critical, though I have nothing to say against his mathematics, so far as it is “pure,” or merely symbolic; for even though we might not, with Macaulay, say that it is well known to every schoolboy, or was even known to Macaulay himself, it would be obvious enough to every modern-side schoolboy who has got as far as “conic sections”; provided he was willing to take some of Dr. Robb’s technical terms in a more or less Pickwickian sense.