A little over 2,200 years ago, the Roman navy attacked the Greek port city of Syracuse. According to some ancient historians, the Greeks defended themselves with an ingenious weapon called a "burning mirror": a polished copper surface curved to focus the Sun's rays onto Roman ships, causing them to catch fire. However, we have several reasons to suspect that the story of the burning mirror is just a myth and the Greeks of Syracuse never really built such a device.
First, the ancient Greeks were not technologically advanced enough to make such a device. A mirror that would focus sunlight with sufficient intensity to set ships on fire would have to be several meters wide. Moreover, the mirror would have to have a very precise parabolic curvature (a curvature derived from a geometric shape known as the parabola). The technology for manufacturing a large sheet of copper with such specifications did not exist in the ancient world.
Second, the burning mirror would have taken a long time to set the ships on fire. In an experiment conducted to determine whether a burning mirror was feasible, a device concentrating the Sun's rays on a wooden object 30 meters away took ten minutes to set the object on fire; and during that time, the object had to be unmoving. It is unlikely that the Roman ships stayed perfectly still for that much time. Such a weapon would therefore have been very impractical and ineffective.
Third, a burning mirror does not seem like an improvement on a weapon that the Greeks already had: flaming arrows. Shooting at an enemy's ships with flaming arrows was a common way of setting the ships on fire. The burning mirror and flaming arrows would have been effective at about the same distance. So the Greeks had no reason to build a weapon like a burning mirror.
Now listen to part of a lecture on the topic you just read about.
The claims that the burning mirror would have been impractical and technologically impossible are unconvincing.
First, the Greeks did not need to form a single sheet of copper to make a large burning mirror. An experiment has shown that dozens of small, individually flat pieces of polished copper could be arranged into a parabolic shape and form a large burning mirror. The Greek mathematicians knew the properties of the parabola and so could have directed the assembly of many small mirror pieces into the parabolic shape.
Second, about how long it would take to set a ship on fire with a burning mirror. The experiment the reading selection mentions assumes that the burning mirror was used to set the wood of the boat on fire—that's what takes ten minutes. But the Roman boats were not made just of wood. There were other materials involved as well. For example, to seal the spaces between wooden boards and make them waterproof, the ancient boat builders used a sticky substance called pitch.
Pitch catches fire very quickly. An experiment showed that pitch could be set on fire by a burning mirror in seconds. And once the pitch was burning, the fire would spread to the wood—even if the ship was moving. So, a burning mirror could have worked quickly enough to be an effective weapon.
Third, why bother with a burning mirror instead of flaming arrows? Well, Roman soldiers were familiar with flaming arrows and would have been watching for them and were ready to put out the fires they might cause. But you cannot see the burning rays from a mirror. You just see the mirror. But then suddenly and magically a fire starts at some unobserved place on the ship. That would have been much more surprising—and therefore much more effective—than a flaming arrow.
The listening content totally opposes the reading passage in the existence of the burning mirror.
Firstly, the reading says that the ancient Greeks were not technologically advanced to build the mirror, given that the mirror had to be designed with a wide shape and parabolic curvature. Yet, the speaker argues that Greeks mathematicians knew the properties of parabola, so they could build such mirror using many small flat pieces of copper to assemble and form.
Secondly, the reading implies that the mirror would have taken a long time to set the ships on fire based on an experiment that shows that the 30-meter-away mirror concentrating sun rays takes 10 minutes to set the object on fire. The lecturer, however, asserts that the pitch, a material that was incorporated into Romans’ ships, made ships catch on fire within several minutes. Moreover, the reading talks about the fact that when the mirror was concentrating sun’s rays, ships were unmoving, so it was unlikely that Romans’ ships would stay until setting on fire. However, the speaker disputes it and stresses that even moving, the pitch could spread fire quickly.
Lastly, the reading suggests that Greeks use the flaming arrow instead of the burning mirror since the effectiveness of the flaming arrow and the burning mirror are the same. Nonetheless, the speaker defends that Romans were familiar with the flaming arrow, so when they saw that the flaming arrow makes ships catch on fire, they could put out the fire quickly. On the other hand, Romans were unfamiliar with the burning mirror, so when the fire started, they would feel surprising.
Thus, the reading and the listening are contradictory in the issue of the burning mirror.
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Grammar and spelling errors:
Line 3, column 367, Rule ID: WHITESPACE_RULE
Message: Possible typo: you repeated a whitespace
Suggestion:
... pieces of copper to assemble and form. Secondly, the reading implies that the m...
^^^^^
Line 7, column 484, Rule ID: WHITESPACE_RULE
Message: Possible typo: you repeated a whitespace
Suggestion:
...re started, they would feel surprising. Thus, the reading and the listening are ...
^^^^^
Transition Words or Phrases used:
first, firstly, however, lastly, moreover, nonetheless, second, secondly, so, thus, on the other hand
Attributes: Values AverageValues Percentages(Values/AverageValues)% => Comments
Performance on Part of Speech:
To be verbs : 10.0 10.4613686534 96% => OK
Auxiliary verbs: 6.0 5.04856512141 119% => OK
Conjunction : 5.0 7.30242825607 68% => OK
Relative clauses : 17.0 12.0772626932 141% => OK
Pronoun: 20.0 22.412803532 89% => OK
Preposition: 29.0 30.3222958057 96% => OK
Nominalization: 2.0 5.01324503311 40% => More nominalizations (nouns with a suffix like: tion ment ence ance) wanted.
Performance on vocabulary words:
No of characters: 1447.0 1373.03311258 105% => OK
No of words: 282.0 270.72406181 104% => OK
Chars per words: 5.13120567376 5.08290768461 101% => OK
Fourth root words length: 4.09790868904 4.04702891845 101% => OK
Word Length SD: 2.53886098474 2.5805825403 98% => OK
Unique words: 143.0 145.348785872 98% => OK
Unique words percentage: 0.507092198582 0.540411800872 94% => More unique words wanted or less content wanted.
syllable_count: 423.9 419.366225166 101% => OK
avg_syllables_per_word: 1.5 1.55342163355 97% => OK
A sentence (or a clause, phrase) starts by:
Pronoun: 2.0 3.25607064018 61% => OK
Article: 12.0 8.23620309051 146% => OK
Subordination: 0.0 1.25165562914 0% => More adverbial clause wanted.
Conjunction: 0.0 1.51434878587 0% => OK
Preposition: 1.0 2.5761589404 39% => More preposition wanted as sentence beginning.
Performance on sentences:
How many sentences: 11.0 13.0662251656 84% => Need more sentences. Double check the format of sentences, make sure there is a space between two sentences, or have enough periods. And also check the lengths of sentences, maybe they are too long.
Sentence length: 25.0 21.2450331126 118% => OK
Sentence length SD: 44.4099981297 49.2860985944 90% => OK
Chars per sentence: 131.545454545 110.228320801 119% => OK
Words per sentence: 25.6363636364 21.698381199 118% => OK
Discourse Markers: 9.18181818182 7.06452816374 130% => OK
Paragraphs: 5.0 4.09492273731 122% => OK
Language errors: 2.0 4.19205298013 48% => OK
Sentences with positive sentiment : 1.0 4.33554083885 23% => More positive sentences wanted.
Sentences with negative sentiment : 8.0 4.45695364238 179% => OK
Sentences with neutral sentiment: 2.0 4.27373068433 47% => OK
What are sentences with positive/Negative/neutral sentiment?
Coherence and Cohesion:
Essay topic to essay body coherence: 0.154286751101 0.272083759551 57% => OK
Sentence topic coherence: 0.0673829963356 0.0996497079465 68% => OK
Sentence topic coherence SD: 0.0366035977575 0.0662205650399 55% => OK
Paragraph topic coherence: 0.0908571804785 0.162205337803 56% => OK
Paragraph topic coherence SD: 0.0322778422378 0.0443174109184 73% => OK
Essay readability:
automated_readability_index: 15.6 13.3589403974 117% => OK
flesch_reading_ease: 54.56 53.8541721854 101% => OK
smog_index: 8.8 5.55761589404 158% => OK
flesch_kincaid_grade: 11.9 11.0289183223 108% => OK
coleman_liau_index: 12.77 12.2367328918 104% => OK
dale_chall_readability_score: 8.35 8.42419426049 99% => OK
difficult_words: 62.0 63.6247240618 97% => OK
linsear_write_formula: 14.0 10.7273730684 131% => OK
gunning_fog: 12.0 10.498013245 114% => OK
text_standard: 12.0 11.2008830022 107% => OK
What are above readability scores?
---------------------
Rates: 80.0 out of 100
Scores by essay e-grader: 24.0 Out of 30
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Note: the e-grader does NOT examine the meaning of words and ideas. VIP users will receive further evaluations by advanced module of e-grader and human graders.