The alleged Change of Colour in Sirius.
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  In an earlier communication of mine (The Observatory, vol. x. p. 104, to which Miss Clarke does me the honour to refer in her 'System of the Stars,' p. 146), I called attention to the mistake (pointed out by Schjellerup) which had probably been made in supposing that Ptolemy had classed Sirius amongst the red or reddish (ὐπόκιῥῤοι) stars. But later (particularly Roman) writers are generally regarded as having done so. I am extremely obliged to Prof. 0om, of Lisbon, for calling my attention to the fact that a main point in Prof. Schiaparelli’s paper is the strong probability that by Canicula these writers do not mean Sirius, but Procyon.
  After a full discussion of the passage in the ‘ Almagest,’ Prof. Schiaparelli goes on to speak of the Roman writers. Cicero, Germanicus, and Avienus published translations of Aratus †, and in these the expression “rutilus” is applied to the light of Sirius. But this word does not necessarily mean red or even any tint of colour; Cicero applies it in the same translation to the body of the constellation Virgo, evidently meaning simply “ bright,” as Schiaparelli remarks “senza designazione di colore speciale.” The decided attribution of a red colour to the star called by them Canicula is to be found in Horace and Seneca. The former speaks of “ rubra Canicula ” in Sat. ii. 5 ; the latter, in his ‘ Quaestiones Naturales,’ i. 1, says that it is not wonderful there should be varieties of colour on the Earth since such exist also in the, heavens, “sed acrior sit caniculae rubor, Martis remissior,” which has been generally taken to mean that Sirius is more red than Mars. But, as I remarked before, Prof. Schiaparelli gives reasons for believing that Canicula means Procyon, not Sirius. It will be sufficient here to quote the passage to which he refers from Hyginus : “ . . . . canem autem sua appellatione et specie caniculam dixerunt ; ques a Graecis quod ante majorem Canem oritur Procyon appellatur.”
  In his second paper, Prof. Schiaparelli states that when he wrote his first he had not seen those of Prof. See. He therefore now goes over the same passages as the latter had done, and contends that in the other ancient authorities where Sirius is alluded to, the epithets applied to it refer to its brightness, not its colour; thus in the ‘Iliad,’ where it is compared to the arms of warriors (Diomed, Hector, and Achilles), and likened to the appearance of fire, what is meant is not redness, but power of light, inextinguishableness, as the poet himself expresses it, ἀκάματον πῦρ (II. V. 4).
  Prof. Schiaparelli’s arguments appear to be very convincing; but is there not another difficulty introduced with regard to the passages from the Roman writers, especially Seneca? Must we take him to mean that Procyon was red, and, according to Seneca, of a hue “acrior” than that of Mars? Perhaps on this point I may again refer to my letter to you of Feb. 1887 (vol. x. p. 104), at the end of which the suggestion is mentioned that the true reading is not “rubor,” but “fulgor.” Not even Sirius is so bright as Mars when near opposition, but the comparison may have been made when the planet was near quadrature.
Yours faithfully,
Blackheath, 1902, Feb. 3.