science

Third principal meridian

Third principal meridian is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Third principal meridian rather than just read about it. In short: The third principal meridian begins at the mouth of the Ohio River and extends north to the northern boundary of the state of Illinois, and with the base line in latitude 38° 28′ 20″, governs the surveys in the state east of the third principal meridian, with the exception of those projected from the second principal meridian, and the surveys on the west, to the Illinois River. This meridian is nearly coincident wit…

Key takeaways

Third principal meridian belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Third principal meridian to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Third principal meridian from memory before moving on to harder problems.

Reference excerpt

The third principal meridian begins at the mouth of the Ohio River and extends north to the northern boundary of the state of Illinois, and with the base line in latitude 38° 28′ 20″, governs the surveys in the state east of the third principal meridian, with the exception of those projected from the second principal meridian, and the surveys on the west, to the Illinois River. This meridian is nearly coincident with 89° 10′ 15″ of west longitude from Greenwich.

External links "The Third Principal Meridian". Principal Meridian Project. Retrieved 2012-09-15. "Third Principal Meridian". The Center for Land Use Interpretation. Retrieved 2012-09-15. "Historic Marker: The Third Principal Meridian". Illinois State Historical Society. Retrieved 2016-10-28.

Sources Raymond, William Galt (1914). Plane Surveying for Use in the Classroom and Field (via Internet Archive). New York: American Book Company. "Chapter Five: Land Surveying". Survey Manual (PDF). Springfield, Illinois: Illinois Department of Transportation, Bureau of Design and Environment. 2003-02-28. p. 5. Archived from the original (PDF) on 2011-05-25. Retrieved 2008-10-30.

Illustrations

Worked examples

Example 1 — a first encounter with Third principal meridian

Start with the simplest possible case. Write down what Third principal meridian claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Third principal meridian before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Third principal meridian ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Third principal meridian

In research: Third principal meridian appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Third principal meridian in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Third principal meridian is common in secondary-school and first-year university syllabi. It links to neighbouring topics Meridians (geography), Meridians and base lines of the United States, so understanding it makes those chapters shorter.
In everyday life: Look for Third principal meridian outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Third principal meridian in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Third principal meridian means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Third principal meridian out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Third principal meridian in simple terms?

Why does Third principal meridian matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Third principal meridian?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Third principal meridian.