A historical example of rhetoric and figurative language in making a scientific argument,
"When I was with you last year … I first began to understand what sort of task and how great a difficulty it was to recall this queen of mathematics, astronomy, to her palace, as she deserved, and to restore the boundaries of her kingdom. …
But when I see that my teacher always has before his eyes the observations of all ages together with his own, assembled in order as in catalogues; then when some conclusion must be drawn or contribution made to the science and its principles, he proceeds from the earliest observations to his own, seeking the mutual relationship which harmonises them all; the results thus obtained by correct inference under the guidance of Urania he then compares with the hypotheses of Ptolemy and the ancients; and having made a most careful examination of these hypotheses, he finds that astronomical proof requires their rejection; he assumes new hypotheses, not indeed without divine inspiration and the favour of the gods; by applying mathematics, he geometrically establishes the conclusions which can be drawn from them by correct inference; he then harmonises the ancient observations and his own with the hypotheses which he has adopted; and after performing all these operations he finally writes down the laws of astronomy–when, I say, I behold this procedure, I think that Plato must be understood as follows.
The mathematician who studies the motions of the stars is surely like a blind man who, with only a staff to guide him, must make a great, endless, hazardous journey that winds through innumerable desolate places. What will be the result? Proceeding anxiously for a while and groping his way with his staff, he will at some time, leaning upon it, cry despair to heaven, earth, and all the gods to aid him in his misery. God will permit him to try his strength for a period of years, that he may in the end learn that he cannot be rescued from threatening danger by his staff. Then God compassionately stretches forth His hand to the despairing man, and with His hand conducts him to the desired goal.
The staff of the astronomer is mathematics or geometry, by which he ventures at first to test the road and press on. For in the examination from afar of those divine objects so remote from us, of what avail is the strength of the human mind? Of what avail dim-sighted eyes? Accordingly, if God in His kindness had not endowed the astronomer with heroic ambitions and led him by the hand, as it were, along a road otherwise inaccessible to the human intellect, the astronomer would not be, I think, in any respect better circumstanced and more fortunate than the blind man, save that trusting in his reason and offering divine honours to his staff, he will one day rejoice in the recall of Urania from the underworld. When, however, he considers the matter aright, he will perceive that he is not more blessed than Orpheus, who was aware that Eurydice was following him as he danced his way up from Orcus; but when he reached the jaws of Avernus, she whom he dearly longed to possess disappeared from view and descended once more to the infernal regions. Let us then examine, as we set out to do, my teacher's hypotheses for the remaining planets, to see whether with unremitting devotion and under the guidance of God, he has led Urania back to the upper world and restored her to her place of honour."
Rheticus (1959) The Narratio Prima (1539, Translated by. E. Rosen), in Three Copernican Treatises (Ed. E. Rosen) Dover Publications (pp.107-196).
In this quite long quotation, Rheticus personifies astronomy; uses an analogy between the state of astronomy and being in the underworld, and another about the astronomer being like a blind man on a long journey.
According to Rheticus the task of the astronomer (making the journey without sight) is beyond human intellect, even with the aid of the blind man's staff (mathematical tools), unless given insight by God. Today it is generally frowned upon to invoke supernatural explanations within science – but, at the time he was writing, investigations into nature (considered as God's creation) were seen as (not just compatible with religious belief, but) a form of pious behaviour.
The analogy of Copernicus by reorganising astronomical data using a model where the earth moves but the sun is fixed being like restoring astronomy from the underworld uses a cultural reference that Rheticus can assume (as it would have been part of the curriculum throughout Europe, and so familiar to literate readers) his reader will appreciate – the myth of Orpheus who travelled down into Hades to beg for the restoration of his wife to the land of the living. Not all modern readers will appreciate this reference, potentially making the analogy rather obscure today.
Read examples of scientific analogies
At the start of the quote Rheticus refers to astronomy as a queen, and to 'her' palace and 'her' kingdom. This is to treat astronomy as a person – personification.
Later he refers to Urania, traditionally one of the Greek muses, associated with astronomy (and astrology), and sometimes used to stand for astronomy: so the references to recalling Urania, leading her from the underworld (like Orpheus leading Eurydice) and restoring 'her to her place of honour' can be understood as a continuation of the personification of astronomy.
Read about personification in science texts
Read about examples of personifying nature
Read about other examples of personification
