RighiniG., “New Light on Galileo's Lunar Observations”, in BonelliM. L. and SheaW. R., Reason, experiment, and mysticism in the Scientific Revolution (New York, 1975), especially p. 75. The criticism by GingerichO., mentioned below, is in the same volume, especially p. 87.
2.
Since this and all other letters cited are arranged chronologically in the National Edition of Galileo'sOpere, vol. x, page references are omitted here.
3.
This is only one of several instances in which the context shows that Galileo sometimes wrote “diameter” for “semi-diameter”.
4.
Before Professor Righini's acute discussion of the astronomical evidence for lunar observations by Galileo during December 1609 I supposed that all Galileo's celestial observations dated from 7 January 1610 or very shortly before, and that they had awaited construction of a 30-power telescope. As will be seen, I now question whether Galileo ever used so strong an instrument for astronomical purposes.
5.
This wording suggests that Gallieo had been writing in response to a specific request, as did also the abrupt beginning to the letter. Antonio Favaro supposed the intended recipient to have been Antonio de' Medici. A more likely candidate in my opinion was Enea Piccolomini, who may have been shown some of the actual observations on a visit to Padua. The evidence for this, however, is not germane to the immediate issue.
6.
DrakeS. and O'MalleyC. D., The controversy on the comets of 1618 (Philadelphia, 1960), 319.
7.
“Let us cause our vision to pass through … a tiny opening which we may leave between the palm of our hand and the fingers, clenching the fist and bringing it to the eye, or through a hole made by a fine needle in a card” (Galileo, Dialogue (trans. DrakeS., Berkeley, 1953), 337).
8.
“It is necessary to prepare quite a perfect telescope which will show all objects bright, distinct, and free from all haziness, while magnifying them at least four hundred times and showing them twenty times closer” (DrakeS., Discoveries and opinions of Galileo (New York, 1957), 30).
9.
It is precisely this candid confession and some related admissions in Galileo's published account that give it a plausibility lacking in Simon Mayr's account when in 1614 he claimed prior discovery of Jupiter's satellites.
10.
This notation and the others through 12 January have been taken from the manuscript journal of observations begun on the night of 15 January, the original page from which he copied them into the journal being lost.
11.
MeeusJ., “Galileo's First Records of Jupiter's Satellites”, Sky and telescope (February, 1964), [105–6], a truly classic contribution to Galilean scholarship.
12.
DrakeS., “Galileo Gleanings xiii, An unpublished fragment …” (Physis, iv (1962), 342–4).
13.
In his published account Galileo placed the completed hypothesis on 11 January as implied in the journal entry for that night, without mentioning any intermediate step.
14.
In the Sidereus nuncius the diagram showed the westernmost as below the line, while the text described its neighbour as above the line. The journal diagram was subject to either interpretation; Galileo's probable reason for preferring the latter description depended on the positions he showed for the 13th and the assumption that the two most westerly were the same stars on both nights. Positive identification of any given satellite on any night required much further study.
