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A fish-eye view of the Red sea in Israel, early spring
My Encounter with the Firmament
The Torah describes God’s fashioning the firmament (רקיע) on the second day of creation. This piece of the universe, however, doesn’t actually exist—a problem obfuscated in my yeshiva education.
by Dr Oren Fass, M.D.
(TheTorah.com)

Of all the vexing problems modern cosmology poses for the first chapter of Genesis, such as the insufficient biblical timeline of 6 days (as opposed to billions of years) until the appearance of humans, or vegetative bloom before the sun and photosynthesis, the most acute for me is God’s creation of the firmament (רקיע; rakia) on the second day.
If you are unfamiliar with the firmament, then imagine for a moment the horizon, where the earth appears to meet with the sky. Only try and picture it as a connecting point between two solids: a flat plate like earth, and a rigid dome like an upside down bowl that vaults it, blue as ocean, from the vast stores of water it contains.  This is what the Bible is describing when it refers to הָרָקִיעַ, traditionally rendered in English Bibles as “the firmament” (from the Latinfirmamentum meaning “support”).
If you can entertain this notion, and feel yourself underneath this massive curved wall of heaven, straining under the weight of the rainwater it holds back, then you are living on the earth our sages knew, for this is the world, the universe, of which the Bible conceived:
בראשית א:ו וַיֹּאמֶר אֱלֹהִים יְהִי רָקִיעַ בְּתוֹךְ הַמָּיִם וִיהִי מַבְדִּיל בֵּין מַיִם לָמָיִם.א:ז וַיַּעַשׂ אֱלֹהִים אֶת הָרָקִיעַ וַיַּבְדֵּל בֵּין הַמַּיִם אֲשֶׁר מִתַּחַת לָרָקִיעַ וּבֵין הַמַּיִם אֲשֶׁר מֵעַל לָרָקִיעַ וַיְהִי כֵן. א:ח וַיִּקְרָא אֱלֹהִים לָרָקִיעַ שָׁמָיִם… 
Gen 1:6 God said, “Let there be a firmament in the midst of the water, that it may separate water from water.”  1:7 God made the firmament, and it separated the water which was below the firmament from the water which was above the firmament. And it was so. 1:8 God called the firmament Sky…
The idea of a firmament is entirely contradictory to modern planetary science; yet there God is, in our Torah, spending all of creation day number two fashioning it.
The Pre-Modern Belief in a Firmament
The idea of the sky above us as a solid structure is shared by almost all pre-modern human cultures. It is best understood as a product of the pre-scientific mind, attempting to make sense of what it sees and offering an intuitive, though factually incorrect, account.
The sky is blue because it is full of water, like the sea.[1] Water doesn’t fall on us because something is holding it up, and that something is transparent, since we can see the blue hue of the liquid behind it.[2] This barrier is dome shaped, since we see the heavens above curving into the horizon and meeting the flat earth.
This understanding is so ubiquitous that some anthropologists consider it a “general human belief.”[3] As Paul Seely, a Bible scholar who works on the intersection of ANE literature and science, writes:
Apart from a scientific education, it is just too natural for people to think of the sky as something solid.[4]
Cultural legends describing the dome are abundant enough to include arrows being shot into the firmament and lodging there (Japan, Native America, Chuckchee), adventurers climbing up to the sky (India), people climbing up through a hole in the firmament (Navaho) or tumbling down through one (Seneca), and heroes sailing a ship to the place where the sky meets the earth (Buriat), and where the firmament is so low that ship masts can end up scraping it.[5]
This belief in a solid firmament was standard among the people of the ANE, who distinguished between the “atmosphere” in which we live and the solid sky above. In Sumerian mythology, An is the god of the sky/firmament, whereas Enlil (literally, “Lord of Wind”[6]) is the god of what happens between the ground (controlled by En.Ki, “Lord of the Earth”) and the firmament.
In Egypt, the sky is pictured as the goddess Nut, with stars all over her body. Her hands rest on one side of the earth and her legs on the other, and Shu, the god of air, stretches his hands in the air to hold her up. In Babylonian creation story Enuma Elish (tablet 5), Marduk kills the giant creator goddess Tiamat, and uses part of her corpse to create the earth and the other to create the sky:
He set her thigh to make fast the sky.With half of her he made a roof; he fixed the earth.[7]
In short, to the ancients the universe was a terrarium of sorts, a carefully preserved space that was fashioned for them by a creator or creators, a “bubble” in endless waters, in which the terrifying calamity of certain flooding was prevented by walls that vaulted above them, the floodgates (אֲרֻבֹּת הַשָּׁמַיִם) of Genesis 7:11. Thus, to the ancient Israelites, the depiction of the second day of creation was natural: the creator was building for them the firmament, the great dome of the sky, and protecting them from being drowned by the waters above.
The ancient conception of  the universe. Diagram from “A dictionary of the Bible; dealing with its language, literature, and contents, including the Biblical theology;” (1898)

The Pre-Copernican Dome
Every pre-Copernican commentator in Judaism who wrote about the rakia knew exactly what it was.[8] The Talmud, for instance, records varying opinions about the thickness of what is clearly a solid firmament; from the seven layer firmaments of Resh Lakish (b. Chagigah 12b), to the two firmaments of R Judah (ibid.), from the finger-width firmament of Rav Joshua ben R Nehemia (Gen. Rab. 4:5), to the “50 year journey” firmament of Rav Judah (j. Berachot2c).
The Rabbis even debate the routes of the sun at night when it leaves the visible sky under the dome, whether it travels either above the firmament or under the earth (Gen. Rab. 6:8; b.Pesachim 94b). The latter possibility leads to the Rabbis forbidding water not drawn before nightfall for matzah baking, lest the sun travel under the plate-like earth and warm the water from underneath before it returns to the dome for morning (b. Pesachim 42a).[9] This is called mayim she-lanu (water that has been left out [lit. rested] and avoided being heated by the sun), still in observance today in certain circles,[10] and it removes the Talmudic understandings of cosmology from mere aggadic speculation into practical halachah.[11]
As modern people, we know that the sun does not heat ground water by traveling underneath a flat earth. After all, the earth is round. The moon, the stars, and the sun are not placed in a dome that rotates about the earth. Rather, the earth revolves around the sun, the stars are distant suns, and the moon orbits around the earth. But our round earth, revolving around a giant sun, and situated in the vast expanse of space in an immense universe, is not the world of the Torah or the Sages. 
What We Have Been Taught
My wife and I were both brought up in Yeshiva Orthodoxy. When discussing this essay with her, she told me that in her senior year of high school in an Orthodox seminary, a sizable amount of time was dedicated to the first and second days of creation. The focal point of this discussion was aimed at highlighting the magnificence of the conversion of nothingness into “something-ness” or matter. This series of lectures involved a great many invocations of avant-garde physics terminology as well as deeper, albeit hidden knowledge. The firmament itself was not described as a dome over a flat earth, and the waters it separated were not waters at all.  It was all a metaphor for a material process of creation outside of our knowledge, and in fact, outside our imaginations, and was somehow tied to these obscure, scientific-sounding processes.
My own educational experience regarding the firmament began in ninth grade in Yeshiva while learning the Talmudic tractate of Nedarim. It was not tied directly to pseudo-science, as was my wife’s training.  When I asked my Rebbi what the firmament was, he replied that it was the “sheath” through which the sun traveled. There was no mention of the premodern beliefs about the earth’s dome. My Rebbi chose to describe a new force of nature, something apparently unknown to science as of yet.
“What is this sheath, and how does anyone know about it?” I wanted to know. The answer from my Rebbi was very direct. The sages knew things that we don’t. My Rebbi’s answer was very familiar to me, as it would be to any student from the Yeshiva system. This is the concept of da’as Torah [12] (דעת תורה): The sages’ immersion in Torah studies provided expertise in worldly knowledge as well, to be trusted above scientific pronouncements (contemporarily regarding evolution).
Not completely satisfied, I returned to my Rebbi again after tracking down Rashi’s comment (Gen 1:6)—which he took from earlier rabbinic texts[13]—about how the rakia was really made on the first day and only congealed on the second, based on a midrashic reading of a verse in Job:
יהי רקיע – יחזק הרקיע. שאף על פי שנבראו שמים ביום ראשון, עדיין לחים היו, וקרשו בשני מגערת הקדוש ברוך הוא באומרו יהי רקיע וזהו שכתוב (איוב כו יא) עמודי שמים ירופפו כל יום ראשון. ובשני יתמהו מגערתו, כאדם שמשתומם ועומד מגערת המאיים עליו:
“Let there be a firmament” – let the firmament solidify. For even though the heavens were created on the first day, they were still liquid, but they congealed on the second day in response to the Holy One’s roar, when he said “Let there be a firmament.” This is what the verse means (Job 26:11): “The pillars of heaven tremble” – all through the first day, and on the second [they were] “Astounded at His blast” like a person who is stunned and freezes from the roar of someone threatening him.
“How could Rashi know that,” I asked? It was the same answer. Rashi had access to a type of spiritual information that was no longer in existence.[14] We couldn’t know how he knew; we were constrained to read and wonder and pine over what had been lost: the secrets, the deeper understanding of, well, everything.
The concept of yeridos ha-doros (ירידת הדורות; literally, “the descent of the generations”), the idea that every generation farther from the revelation at Sinai has gone down in its spiritual level, meant we had fallen into ignorance over the centuries, and there was no ladder back up. According to my Rebbi, the firmament was some type of energy, or force, that the great sages, but not us, were aware of.
Encountering the Rakia as an Adult
There is no way around this ironclad ideology when one is thirteen and being instructed in yeshiva. I did, however, have one last encounter with the rakia as an adult, while attending a bar mitzvah two years ago on Shabbos Bereishes (שבת בראשית; the Shabbat in which the creation story is read). In a side room, a guest speaker had come prepared to solve all of the cosmological problems of Bereishis. After about thirty minutes, it seemed that a room full of well educated, modern Orthodox men and women were fully satisfied by “days” that didn’t mean days, and “seeds” that arrived on day three but bloomed on day four with the creation of the sun (seeds from outer space were also acceptable).
When I caught the speaker’s eye and asked about the rakia, I caused the lecture to grind to halt. “It’s a fictional structure,” I had said, but looking around the room at surprised faces and questioning eyes, I realized no one other than the speaker understood my question. Rather than answer the question, the speaker challenged me: “Who are you”?[15]
I was terribly embarrassed to introduce myself as an average Joe; I hadn’t written a sefer(traditional Jewish book), attended any type of biblical academic program, or made so much as a podcast, to everyone’s disappointment. After introductions, the speaker informed me that my question was so good, it needed to be answered, after the shiur. True to his word, he found me at the kiddush afterward. “The rakia” he said, “could mean air… or clouds,” he told me in private, and very quickly departed to his next lecture.
Apologetics and the Firmament: Air or Clouds
Modern Jewish audiences are not the first to be disturbed by the imaginary firmament so centrally displayed in the (ostensibly divinely dictated) Bible. Conservative Christianity is equally anxious that such a state of affairs be reconciled.
In response to the Copernican revolution of the 16th century, John Calvin—the French theologian largely responsible for the formation of the Protestant movement, Calvinism—suggested in 1554 that the firmament refers to air or clouds.[16] (Little did the Shabbos speaker know he was quoting John Calvin!) This idea occasionally appears on Orthodox Jewish discussions of this topic, as it did with the speaker in Shul, and was introduced into Orthodoxy by Rav Samson Raphael Hirsch (1808-1888).[17]
Although such answers neatly sidestep the root problem of God creating a nonexistent structure, they create other problems. For instance, the air does not separate “water from water” as the verse states, nor would air or clouds exist prior to the creation of the sun and moon on day (time period) four in any cosmology that wanted to at least pretend to be scientific. 
Additionally, the word rakia simply does not mean air or clouds. Insofar as clouds, the Bible uses the term anan (ענן) or av (עב), not rakia. Moreover, the creation story in Genesis 1 clearly describes that whereas the sun, moon, and stars are placed in the rakia (בִּרְקִיעַ הַשָּׁמַיִם), birds—who fly through the air—are placed below the rakia (עַל פְּנֵי רְקִיעַ הַשָּׁמָיִם; literally “on the face of the heaven’s firmament”). Thus, rakia cannot refer to air.  Moreover, as the Talmud already notes[18] and contemporary biblical lexica such as BDB and HALOT affirm, the etymology of the word rakia connects it with the activity of “hammering out” of a solid material, as would be done to turn tin or copper into a flattened dome. They are obviously not picturing air and clouds.[19]
Perhaps the clearest evidence that clouds or air is not really “the answer” is that no English Chumash/Bible that I have seen uses such a translation. If this were really such a persuasive answer, such a translation would be ubiquitous. I think back to my interaction with the guest speaker two years ago. Why was he only willing to discuss this in private conversation after the lecture was over? It’s because it can’t be offered as a public answer, out loud, since it leads to yet another, deeper problem.
The Infallible Masorah
According to traditional Jewish conceptions, an unbroken tradition (masorah) exists from God at Sinai to our sages to the present (see, e.g., m. Abot 1:1). For centuries, this masorahunderstood the rakia as a solid dome. A modern speaker cannot simply change that based on modern science without bringing up serious questions about the origin of this unbroken chain, especially in the case of the rakia, where the core pronouncements come from the Bible.
Moreover, this same masorah is also responsible for assuring us that what we know about our traditions and our beliefs are true. All proofs and arguments central to the defense of our core faith lead back to the idea of an unbroken chain of information leading to God’s communication with Moses on Mount Sinai.
It is no easy task to walk away from any specific piece of it. It is especially difficult when we have to at once discard part of our masorah, and admit, that immersion in Torah knowledge (da’as Torah) did not produce a correct understanding of the mechanics of the universe, even amongst our greatest sages. Instead, it is an astronomer—not of Jewish lineage—who overturned this image of the universe, and through observation and logic caused the dome of our sages, and our Bible, to disappear.
Why wasn’t this well known fact—the absence of a firmament in modern science—touched upon in my yeshiva experience? Perhaps, because it is difficult to introduce students to the idea that the rabbinic tradition is not absolutely reliable on all matters. To teach students that our Torah was dictated by the Creator Himself, and that the true understanding of this Torah has been passed down through the ages by sages of great sagacity with unprecedented access to the secrets of creation, while at the same time walking to the chalk board to draw a line and a semicircle and declaring this depiction to be the universe of both God and the sages—the same world, in which people feared sailing their ships off the edge—that is some choppy water to navigate through in the first month of the Yeshiva school year, when the beginning ofBereishis is traditionally read!
Thus, the solution has become: obfuscate and don’t discuss the simple meaning of the text. “Issues with Bereishis? What Issues?” has been adopted as the way to go. In fact, rather than presenting these verses as conflicting with science, educators assign them to the realm of the unknown or to descriptions of vague and mysterious scientific processes. Ironically, this turns them into support for da’as Torah (only Rashi could have known about the firmament’s energy!) and a support for the masorah (the sages have always understood what science is barely beginning to grapple with, like the big bang and cosmic energies and quantum physics).
What the Mepharshim Say
So what do the Rabbis mean by saying that the rakia was liquid on the first day and congealed on the second? Genesis Rabbah (Bereishit 4; Theodor-Albeck edition), while discussing the possible meanings of the word shamayim, states the following:
ר’ יצחק אמר שאמים טעון מים, לחלב שהיה נתון בקערה עד שלא תרד לתוכו טיפה אחת שלמסו הוא מרפרף, כיון שתרד לתוכו טיפה אחת שלמסו מיד הוא קופה ועומד כך עמודי שמים ירופפו (איוב כו יא) ניתן בהם את המסו ויהי ערב ויהי בקר יום שני, אתיא כההיא דאמר רב לחים היו [נ]עשים [ביום ראשון][20] ובשיני קרשו.
R. Isaac said: “[Shamayim should be parsed as a command:] Sa-mayim (“carry water”), i.e., it holds up water. [The heavens] were like milk in a dish; until a drip of rennet is put in it, [the milk] sloshes, but once a drop of milk is put in it, [the milk] congeals and becomes solid. This is the meaning of (Job 26:11): ‘The pillars of the heavens were shaky.’ A coagulant was placed in it, “and it was evening and it was morning, day two.” This follows that which Rav said: “They were liquid on day one, and on day two the congealed.”
As noted above, Rashi uses this same verse from Job, only adding that God’s roar is the coagulant, which connects the two parts of the verse to each other. The image of the clearrakia as being made of congealed water makes intuitive sense in pre-modern thinking since clear water is transparent. And thus, on the first day, God lifts up the water, but holds the water up himself. On the second day, God “barks” at the lower layer of water, thereby solidifying it and allowing it to hold up the water in God’s place.
This explanation is likely influenced by the fact that rakia is used as a parallel term forshamayim in Psalm 19:2:
הַשָּׁמַיִם מְסַפְּרִים כְּבוֹד אֵל וּמַעֲשֵׂה יָדָיו מַגִּיד הָרָקִיעַ.
The heavens declare the glory of God, the firmament proclaims His handiwork.
This may also be what lead the 8th century midrashic work, Pirkei de-Rabbi Eliezer (ch. 4) to claim that the rakia was created on day one, since shamayim, which includes the rakia, was created on day one: 
וַהֲלֹא הַשָּׁמַיִם וְהָאָרֶץ נִבְרְאוּ בְּיוֹם רִאשׁוֹן… וְאֵיזֶה רָקִיעַ בָּרָא בְּיוֹם שֵׁנִי?
But the heavens and the earth were already created on the first day … so what kind of firmament was created on day two?…[21]
An even more telling verse comes again from Job, in which Job’s “friend” Elihu describes the creation of the world (Job 37:18):
תַּרְקִיעַ עִמּוֹ לִשְׁחָקִים חֲזָקִים כִּרְאִי מוּצָק.
Can you help him stretch (ר.ק.ע) out the heavens, firm as a mirror of cast metal?
If the stretched out heavens are also the rakia, then in one sense, rakia and shamayim are the same, and in another sense they are not. Putting all this together, Rashi went with the idea that the rakia is substantially the same material as the heavens, namely water, but that God congealed it so that it became “as hard as a mirror of cast metal” but as transparent as glass or clear water.
Interpreting Rashi Honestly: My Devar Torahand the Benefit of Context
As people living in the scientific era, we make arguments about the nature of the universe based on empirical study, but, as a general rule, this is not how scientific arguments worked in premodern times. In medieval times especially, it was perfectly acceptable to argue a scientific theory based on deductions from biblical texts, as we see here. Moreover, the arguments put forth above only make sense if we accept that these scholars understood the rakia in its simple sense, a large blue barrier holding up the heavenly waters.
When we try to “modernize” the rakia, thinking of it as some sort of mystical energy, or as clouds or air, why these commentators are interested in a firmament or other support already present on the first day becomes inexplicable. What for? Why would the world need a cloud or some mysterious energy on day one more than on day two?
But when we see the universe in their own terms, with waters above that crash down if not held in place, then it becomes clear that having a separate “heaven and earth” on the first day of creation mandates some type of partition; if there is a shamayim (heavenly waters) separated from earth, there must be a firmament of sorts to hold it up. This follows logically when we understand the nature of the pre-modern universe. Thus, ironically, we can only understand and appreciate the insights of our mephorshim (traditional commentators) when we view them through a pre-modern lens, and not when we “force them to speak” in contemporary scientific parlance.
Teaching Torah in the Age of Google
I understand the yeshiva world’s simple calculation in avoiding discussing the rakia honestly. The odds that the typical ba’al habos (בעל הבית; average working stiff) will connect these verses with ANE concepts of the universe is low. It may thus be reasoned to be well worth the risk to avoid this altogether, compared to the alternative: exposing entire classrooms to the problem thereby “unnecessarily” challenging these young adults. But this strategy doesn’t always work; it didn’t for me. 
As I eventually continued to explore Judaism outside of the yeshiva bubble and realized what had been hidden from me—the rakia is only one illustrative example—I was disheartened. I felt like I was “taken in” by the concepts of da’as Torah and the masorah as promoted by educators, and left feeling foolish. It took me some time, long after I finished high school, before I came into contact with contemporary notions of biblical scholarship that make concepts like the rakia accessible in a logical manner.
It has been a few decades since my high school experience, and it is no longer difficult to find information about what the Bible means in its ANE context that will quickly contradict whatever apologetics one may hear in yeshiva. Perhaps the community of educators within the system should consider a new strategy. After all, a lazy lunchtime Google search will bring anyone with a passing curiosity a dozen sources with everything the yeshiva educators where hoping students would never find out about the rakia and many other challenging topics. If this piece can be a source for a young student such as I was, trying to figure out a path through the contradictions, for my part, I’m happy to add one more.
_____________________
NOTES
[1] This seems to be the idea in Gen 1, though Exod 24:10 may imply a different explanation, namely that the sky is blue because it is made of lapis lazuli.
[2] Alternatively, it could be blue because it is made of the same substance as the water, only solid. See discussion of Rashi later on.
[3] Gudmund Hatt, Asiatic Influences in American Folklore (Copenhagen, 1949), 50, quoted in, Paul H. Seely: “The Firmament and the Water above Part I: The Meaning of Raqiaʿ in Gen 1:6-8,” Westminster Theological Journal 53 (Fall 1991), 227-240 [231].
[4] Seely, “The Firmament 1,” 231. 
[5] Seely: “The Firmament 1,” 228-231.   
[6] Alternatively “Lord of Storm.”
[7] Translation from, Stephanie Dalley, Myths from Mesopotamia, rev. ed. (Oxford World’s Classics; Oxford: Oxford University Press, 2000 [1989]), 257. For a discussion of where the conception of the world in Gen 1 fits with other ANE conceptions, see Othmar Keel and Silvia Schroer, Creation: Biblical Theologies in the Context of the Ancient Near East (Winona Lake: Eisenbrauns, 2015), 78-84.
[8] Natan Slifkin, “The Sun’s Path at Night,” Rationalist Judaism (2010).    
[9] See discussion in, Moshe Simon-Shoshan, “The Heavens Proclaim the Glory of God – A Study in Rabbinic Cosmology,” Bechol Derakhekha De’ehu 20 (2008): 67-96 [82-83]. 
[10]  And it is still causing traffic jams in Israel to get the water the day before matzah is baked. For other modern manifestations of this law, see the Youtube video, Dorog Rebbe at mayim she-lanu 5776, and Yochanan Donn, “Is New York Targeting Mayim Shelanu?”HaModia (March 20, 2013).
[11] By the time we reach Rambam’s era (13th cent), the firmament is imagined as more complex. In his Guide of the Perplexed (2:30), Rambam rejects the idea of a dome holding up heavenly waters (he says the water isn’t really water) and reimagines the dome to better fit to Aristotelian musings, namely as a huge solid dome containing a complex set of spherical orbits in which the planets move. In fact, Rambam uses the firmament and its spheres for planetary orbits as one of his rational proofs of divine existence. See discussion in, Micah Goodman, Maimonides and the Book That Changed Judaism: Secrets of “The Guide for the Perplexed” (Philadelphia: JPS, 2015), 8. Thus, even Rambam, Judaism’s philosophically literate rationalist, accepts that the rakia is a physical dome in the sky, which returns us to our difficulties, for there is no such dome.
[12] Slifkin, Natan. “The Making of Haredim,” Rationalist Judaism (2012): 9-10
[13] j. Berachot 1:1:
רב אמר לחים היו שמים ביום הראשון ובשני קרשו רב אמר יהי רקיע יחזק הרקיע יקרש הרקיע יגלד הרקיע ימתח הרקיע
Rav said: “The heavens were liquid on the first day and on the second day they congealed.” Rav said: “‘Let the firmament be’ – let the firmament congeal, let the firmament coagulate, let the firmament be spread thin.”
See also R. Isaac’s position about the meaning of shamayim in Genesis Rabbah (Bereishit 4) which I discuss below. 
[14] This claim has long been made about Rashi in particular. See discussion in, Yonatan Kolatch, Masters of the Word: Traditional Jewish Bible Commentary from the First Through Tenth Centuries, vol. 2 (Jersey City: Ktav, 2007) 57.
[15] I consider it odd that the fact that I knew about the problem with the firmament made me a person of note. I don’t know if I was supposed to be a hero or villain, but in 2015 that knowledge was not expected, at least by this particular speaker, to be common knowledge, nor did it appear to be common knowledge to a group of Orthodox people gathered out of scientific interest in Berieshis.
[16] J. Calvin, Genesis (Grand Rapids: Eerdmans, 1948) 78-79. This approach continued in some circles from then until modern times. From the eighteenth century, e.g., A. Clarke, The Old Testament (New York: Hunt & Eaton, n.d.) 1.31. From the nineteenth century, e.g., G. Bush, Notes on the Book of Genesis, (New York: Ivison, Phinney, 1860) 33; R. S. Candlish,Commentary on Genesis (1868; repr. Grand Rapids: Zondervan) 25. From this century, e.g., C. E Keil and E Delitzsch, Biblical Commentary on the Old Testament, The Pentateuch(Grand Rapids: Eerdmans, 1949) 1.52; A. R. Fausset and D. Brown, A Commentary on the Old and New Testaments (Grand Rapids: Eerdmans, 1948) 5; H. L. Ellison and D. E Payne, “Genesis,” in The International Bible Commentary (ed. E E Bruce; Grand Rapids: Zondervan, 1979), 115. 
[17]  Commentary to Genesis 1:6; cf. Rabbi Akiva Eiger, in his note to the phrase u’vokeya chalonei rakia in Siddur Otzar HaTefillos p. 672, and Maharzav to Midrash Bereishis Rabbah 6:8. For discussion of these and other sources, see Natan Slifkin, “What Firmament Really Is,” Rationalist Judaism (2011).  
[18] See, e.g., R. Yudah ben Pazi’s comment in j. Berachot 1:1.
[19] See discussion in, E. J. Young, Studies in Genesis One (Philadelphia: Presbyterian & Reformed, 1964), 90 n. 94.
[20] Albeck’s emendation as per the earlier iteration of Rav’s position in Genesis Rabbah (vol. 1, p. 26).
[21] The text continues by midrashically reinterpreting the verse entirely:
רַבִּי אֱלִיעֶזֶר אוֹמֵר רָקִיעַ שֶׁעַל רָאשֵׁי אַרְבַּע הַחַיּוֹת, שֶׁנֶּאֱמַר [יחזקאל א, כב] וּדְמוּת עַל רָאשֵׁי הַחַיָּה רָקִיעַ כְּעֵין הַקֶּרַח הַנּוֹרָא.
Rabbi Eliezer says: “It was the firmament that sits atop the four creatures [Ezekiel saw in his vision of the chariot], as it says (Ezek 1:22): ‘Above the heads of the creatures was a form: an expanse, with an awe-inspiring gleam as of crystal.’”