Rabbi Slifkin is wont to cite the writings of a Christian evangelist, Paul Seeley. We have already seen that Seeley claimed that standard Hebrew lexica understand the rakia to be a solid dome, as opposed to an atmospheric expanse, apparently oblivious to the Radak’s classic Sefer HaShorashim, which defines the “strength” of the rakia in the Iyov verse otherwise, and the commentaries of other rishonim. He also asserts that Hebrew understanding of the heavens was perhaps even more naïve and primitive than that of all others. The holy texts of the Jews, he asserts, show they considered the rakia to be a hard, solid entity. He takes such texts literally.
Those who want to read into Chazal’s words that they thought the rakia is a solid, metallic-like material would be happy to see the following Chazal that considers the rakia “silver”:
מדרש רבה במדבר פרשה יב:ד
"עמודיו עשה כסף" (שם י:ג) זה הרקיע כמה דתימא (איוב כו) "עמודי שמים ירופפו."
B’midabar Rabbah 12:4
“His pillars He made כסף (usually translated, “silver”) (Shir HaShirim 3:10). This [reference to “pillars”] is [a reference to] the rakia (sky), as you see it says in Iyov (26:11), “the pillars of the heavens will weaken.”
The Chazal-literalists and mesorah-rejectionists would no doubt bring this as clear evidence that Chazal, along with the ancient Hebrews, naively and primitively thought that the sky is made of silver, and that it thereby keeps keeps the heavens from from falling down.
However, they will be disappointed when they see the continuation of this passage. And—if they will be unbiased enough to study Chazal’s words with the proper mindset the Rambam and others insist we utilize—they will realize that Chazal did not understand the metaphors and similes of the pesukim the crude way asserted by the Seeleys and Slifkins of the world.
ס”עמודיו עשה כסף" (שם י) זה הרקיע כמה דתימא (איוב כו) "עמודי שמים ירופפו." ולמה קרי ליה כסף—שהוא מכסף על כל מעשה בראשית.ס
“His pillars He made כסף (usually translated, “silver”) (Shir HaShirim 3:10). This is the rakia (sky), as you see it says in Iyov (26: ), “the pillars of the heavens will weaken.”
And why are they called “כסף”? —because they cover (מכסף) over all of maaseh breishis (creation).
Note that Chazal did not understand the “pillars” to be things that support the heavens, but a poetical reference to the heavens themselves. Accordingly, "עמודי שמים" is not to be translated, “the pillars of the heavens,” but rather: “the pillar-heavens,” or “the heavenly pillars.”
More to our point, we see that when it came to applying the word "כסף" to the sky, Chazal deviated from the typical translation of כסף as “silver;” and we see how far away from the meaning of anything metallic or solid they took its meaning to be.
We should also note that Chazal speak of the “windows” of the rakia, and the “piercing of the heavens,” in an obviously poetical, non-physical way:
מדרש רבה דברים פרשה ב
... ד"ה ב: לג--“ויתפלל אליו [מנשה] ויעתר לו ויחתר לו." מלמד שהיו מלאכי השרת מסתמין את חלונות של רקיע שלא תעלה תפלתו לשמים. מה עשה הקב"ה? חתר את הרקיע מתחת כסא הכבוד וקיבל את תפלתו וישיבהו ירושלים למלכותו ...
Devarim Rabbah 20
...the angels closed up the windows of the rakia so that his prayer would not go up to heaven…....So the Holy One blessed-be-He ripped open the rakia from under the Throne of Glory and received his prayer …
I think we can agree that by “prayer” Chazal meant the thoughts, intentions, desires, etc. of the person behind the spoken words—nothing physical, not even sound waves, that would require the literal opening of “windows of the sky” to “arise” to Heaven.
And these are not Greco-Arabic- or Renaissance-influenced rishonim rationalizing Chazal. These are Chazal themselves.
—Although academics, if they would admit to this, would no doubt turn around and proclaim that this is Aristotelian-Chazal rationalizing Scripture! But at least we can dispense with Rabbi Slifkin’s claim that Chazal thought the rakia is a hard, solid dome, and the kind of “proofs” he brings for that assertion.
 “Standard Hebrew lexica and a number of modern biblical scholars have defined the raqia (רקיע "firmament") of Gen 1:6-8 as a solid dome over the earth. Conservative scholars from Calvin on down to the present, however, have defined it as an atmospheric expanse” (The Firmament and the Water Above, The Westminster Theological Journal 53  p. 227).
 Although he didn’t actually say “all standard Hebrew lexica defined the rakia of Gen. 1:6-8 as a solid dome over the earth.” But on the other hand, I’m not aware of any that do so.
 “Scientifically naive peoples everywhere have believed the sky was solid, and there is no reason to believe the Hebrews were any less scientifically naive than their neighbors…[O]ne might gather that the early Hebrews were possibly more scientifically naive than their neighbors, but certainly not less so. Similarly, the fact that it was not the Hebrews but their neighbors who led the technological advance from the use of bronze to the use of iron (cf. Josh 17:18; Judg 1:19) suggests, if anything, that the Hebrews were more scientifically naive than their neighbors. It certainly does not suggest that they were less so. Nor do we know of any evidence from biblical times that suggests the Hebrews were ever more scientifically sophisticated than their neighbors. Accordingly, it seems most probable that so far as the physical nature of the sky is concerned, the Hebrews, as a typical scientifically naive people, believed the raqia was solid” (Seeley, p. 234).
Seeley does not mention (at least not here) the acclaimed superior scientific wisdom attributed to King Solomon.
 Jews … tried to figure out how thick it was by employing biblical interpretation (Gen. Rab. 4.5.2). Most tellingly they even tried to calculate scientifically the thickness of the firmament (Pesab. [sic.] 49a [sic.—no doubt a typographical error, the reference should be Pesah. 94a).