Passage:
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 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.
Lecture:
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 know the properties of the parabola and so could have directed the assembly of 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 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 flame arrow.
The passage and the lecture both talk about a specific weapon Greeks used to protect against Roman attacks, called a burning mirror. The author mentions three reasons to express the doubt about the story of using the burning mirror. However, the lecturer believes that these reasons are not convincing.
First of all, the passage claims that Greeks did not have the technology to build this weapon which was composed of a large sheet of copper. On the other hand, the lecturer explains that Greeks did not have to make a single sheet. In fact, the experiment shows that the greek mathematicians might use dozen small mirrors to form a larger one.
Secondly, the passage says that a burning mirror takes a long time to ignite a fire, according to an experiment done on a wooden object. However, the lecturer argues this reason, pointing out that Roman ships were made up of some other materials besides wood, and one of them was the pitch. It would have only taken seconds for the mirror to set the pitch on fire, and the fire would spread to other parts of the ship quickly. Therefore, using the burning mirror could be pragmatic.
Finally, the passage explains that there was no reason to make the burning mirror since its effectiveness was equivalent to flaming arrows. In contrast, the lecturer mentions that Romans were familiar with flaming arrows, but they did not expect the burning mirror. Therefore, Greeks used this mirror as a surprising weapon.
Grammar and spelling errors:
Line 2, column 302, Rule ID: NODT_DOZEN[1]
Message: Use simply: 'a dozen'.
Suggestion: a dozen
...that the greek mathematicians might use dozen small mirrors to form a larger one. S...
^^^^^
Transition Words or Phrases used:
besides, but, finally, first, however, if, second, secondly, so, therefore, in contrast, in fact, first of all, on the other hand
Attributes: Values AverageValues Percentages(Values/AverageValues)% => Comments
Performance on Part of Speech:
To be verbs : 8.0 10.4613686534 76% => OK
Auxiliary verbs: 4.0 5.04856512141 79% => OK
Conjunction : 4.0 7.30242825607 55% => More conjunction wanted.
Relative clauses : 9.0 12.0772626932 75% => More relative clauses wanted.
Pronoun: 16.0 22.412803532 71% => OK
Preposition: 31.0 30.3222958057 102% => 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: 1213.0 1373.03311258 88% => OK
No of words: 249.0 270.72406181 92% => More content wanted.
Chars per words: 4.87148594378 5.08290768461 96% => OK
Fourth root words length: 3.97237131171 4.04702891845 98% => OK
Word Length SD: 2.36403295153 2.5805825403 92% => OK
Unique words: 138.0 145.348785872 95% => More unique words wanted.
Unique words percentage: 0.55421686747 0.540411800872 103% => OK
syllable_count: 368.1 419.366225166 88% => OK
avg_syllables_per_word: 1.5 1.55342163355 97% => OK
A sentence (or a clause, phrase) starts by:
Pronoun: 1.0 3.25607064018 31% => OK
Article: 10.0 8.23620309051 121% => OK
Subordination: 0.0 1.25165562914 0% => More adverbial clause wanted.
Conjunction: 3.0 1.51434878587 198% => OK
Preposition: 4.0 2.5761589404 155% => OK
Performance on sentences:
How many sentences: 13.0 13.0662251656 99% => OK
Sentence length: 19.0 21.2450331126 89% => OK
Sentence length SD: 32.3010982282 49.2860985944 66% => OK
Chars per sentence: 93.3076923077 110.228320801 85% => OK
Words per sentence: 19.1538461538 21.698381199 88% => OK
Discourse Markers: 9.92307692308 7.06452816374 140% => OK
Paragraphs: 4.0 4.09492273731 98% => OK
Language errors: 1.0 4.19205298013 24% => OK
Sentences with positive sentiment : 1.0 4.33554083885 23% => More positive sentences wanted.
Sentences with negative sentiment : 9.0 4.45695364238 202% => Less negative sentences wanted.
Sentences with neutral sentiment: 3.0 4.27373068433 70% => OK
What are sentences with positive/Negative/neutral sentiment?
Coherence and Cohesion:
Essay topic to essay body coherence: 0.210863369222 0.272083759551 77% => OK
Sentence topic coherence: 0.0831843430384 0.0996497079465 83% => OK
Sentence topic coherence SD: 0.0543191472764 0.0662205650399 82% => OK
Paragraph topic coherence: 0.13610627695 0.162205337803 84% => OK
Paragraph topic coherence SD: 0.0197615207118 0.0443174109184 45% => Paragraphs are similar to each other. Some content may get duplicated or it is not exactly right on the topic.
Essay readability:
automated_readability_index: 11.1 13.3589403974 83% => Automated_readability_index is low.
flesch_reading_ease: 60.65 53.8541721854 113% => OK
smog_index: 3.1 5.55761589404 56% => Smog_index is low.
flesch_kincaid_grade: 9.5 11.0289183223 86% => OK
coleman_liau_index: 10.97 12.2367328918 90% => OK
dale_chall_readability_score: 7.62 8.42419426049 90% => OK
difficult_words: 48.0 63.6247240618 75% => More difficult words wanted.
linsear_write_formula: 8.0 10.7273730684 75% => OK
gunning_fog: 9.6 10.498013245 91% => OK
text_standard: 8.0 11.2008830022 71% => OK
What are above readability scores?
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Rates: 63.3333333333 out of 100
Scores by essay e-grader: 19.0 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.