physics

John Herapath

John Herapath is a physics 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 John Herapath rather than just read about it. In short: John Herapath (30 May 1790 – 24 February 1868) was an English physicist who gave a partial account of the kinetic theory of gases in 1820 though it was neglected by the scientific community at the time. He was the cousin of William Herapath, the chemist and William Bird Herapath, the physician who discovered herapathite.

Key takeaways

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

Reference excerpt

John Herapath (30 May 1790 – 24 February 1868) was an English physicist who gave a partial account of the kinetic theory of gases in 1820 though it was neglected by the scientific community at the time. He was the cousin of William Herapath, the chemist and William Bird Herapath, the physician who discovered herapathite. In 1847 he published an early textbook on mathematical physics.

Background

Herapath's scientific interests started with an attempt to provide a mechanistic explanation for gravity. Motivated by his search for a mechanical explanation of gravitation, he started to consider how a system of colliding particles could give rise to action at a distance. In considering the effect of the high temperatures near the Sun on his gravific particles he was led to a relationship between temperature and particle velocity.

Kinetic theory Herapath postulated that the momentum of a particle in a gas is a measure of the absolute temperature of the gas. He used momentum, rather than the kinetic energy on which the later established theory is based, as it seemed to him to avoid some difficulties around whether elastic collisions were possible between indivisible atoms. Apparently ignorant of Daniel Bernoulli's work, he was led to the incorrect, but suggestive, relationship that expresses the product of pressure P and volume V as proportional to the square of his true temperature. The correct relationship is proportional to the absolute temperature, not its square, the error arising from his identification of momentum, rather than energy, with temperature.

Herapath, J. (1816), "On the physical properties of gases", Annals of Philosophy, Robert Baldwin: 56–60 Brush, S. G. (1957), "The Development of the Kinetic Theory of Gases 1. Herapath.", Annals of Science, Taylor & Francis: 188–198 He submitted his ideas in a paper to the Royal Society in 1820 where it was peer reviewed by Sir Humphry Davy. Davy had already sympathised with the view that heat was associated with molecular motion rather than with Joseph Black's caloric theory of heat but he rejected Herapath's paper with some coolness, uncomfortable with the implication that there was an absolute zero of temperature at which all motion ceased. Davy may also have had some distaste for the mechanistic Newtonian picture, influenced as he was by the more holistic philosophy of the Romantic movement. In 1821, Herapath used the assumption that the aether is heated by the bodies and loses density so that other bodies are pushed to these regions of lower density. However, it was shown by Taylor that the decreased density due to thermal expansion is compensated for by the increased speed of the heated particles; therefore, no attraction arises. James Prescott Joule presented a short account of the work in 1848. Meanwhile, Herapath maintained a campaign against Davy and the Royal Society in the correspondence pages of The Times newspaper.

Great Comet of 1831

On 7 January 1831 Herapath was on Hounslow Heath when he sighted a comet. Due to its brilliance, it is one of the great comets. The comet was also observed by Thomas Glanville Taylor at the Madras Observatory.

Railway Journal In 1835 Herapath became editor of The Railway Magazine, which underwent four changes of name during the boom years of railways to become Herapath's Railway Journal in January 1894. It is now published as Railway Gazette International, and is not to be confused with The Railway Magazine which commenced publication in 1897. This gave him some limited opportunity to publish his scientific ideas. In 1836, he published a calculation of the mean molecular speed in a gas based on his kinetic theory and hence the speed of sound. Joule reproduced his results but is usually incorrectly credited as the originator. The name changes were –

Railway magazine May 1835-Feb. 1836 Railway magazine and annals of science Mar. 1836 – Aug. 1839 Railway magazine and steam navigation journal Mar. – Aug. 1839 Railway magazine and commercial journal 17 Aug. 1839 – Dec. 1840 Herapath's railway magazine, commercial journal, and scientific review Jan. 1841 – Dec. 1842 Herapath's railway and commercial journal Jan. 1843 – Dec. 1845 The editions from 1839 to 1895 can be viewed in the National Archives and several issues are also available as e-books, e.g. 1837, 1836–1839 and several in Google books.

Later work He revised his theories in the 1840s, largely based on the experimental work of Thomas Graham and Henri Victor Regnault.

1847: Mathematical Physics; or, the Mathematical Principles of Natural Philosophy, the causes of heat, gaseous elasticity, gravitation, and other great phenomena of nature, Whittaker and company via HathiTrust Herapath died at Catford Bridge, Lewisham on 24 February 1868 and was buried at West Norwood Cemetery.

See also History of thermodynamics List of railroad-related periodicals John James Waterston

References Hutchison, Keith. "Herapath, John". Oxford Dictionary of National Biography (online ed.). Oxford University Press. doi:10.1093/ref:odnb/13010. (Subscription, Wikipedia Library access or UK public library membership required.)

External links Dave Levermore (2001) Neglected Pioneers: John Herapath from University of Maryland

Worked examples

Example 1 — a first encounter with John Herapath

Start with the simplest possible case. Write down what John Herapath claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, 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 John Herapath 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 John Herapath 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 John Herapath

In research: John Herapath appears in physics 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 John Herapath 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: John Herapath is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1790 births, 1820 in science, 1847 in science, so understanding it makes those chapters shorter.
In everyday life: Look for John Herapath 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 John Herapath in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what John Herapath 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 John Herapath out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is John Herapath in simple terms?

Why does John Herapath matter?

Because it connects several physics 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 John Herapath?

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 John Herapath.