Newton's Discovery of the Refraction of Light

Episode Eleven – Achievements of Newton


A chromatic aberration is caused by the failure of the lenses in refractive telescopes to properly focus all colors of light to the same point. This results in a blurred image and colored edges.

Such as that shown below:

See the purplish chromatic aberration.

Newton realized that the lens of any refracting telescope would suffer from the dispersion of light into colors. Which is what causes chromatic aberration.

So, he invented the reflective telescopes, using mirrors to correct this problem.

Most telescopes used today are reflecting telescopes. This is because they are not subject to chromatic aberration, although they do suffer other problems.

They also can be used to help combat the disruptive effects of atmospheric turbulence, which is great for Earth-based telescopes.

It is also easier and cheaper to produce the mirrors used by reflecting telescopes than it to make the lenses used by refractive telescopes.

They are also generally more portable and compact.

They have other advantages, as well as disadvantages. Their disadvantages include the fact that their mirrors require more careful handling than their refractive counterparts. As well as the fact that their mirrors may need occasional readjusting.

But, by and large, reflective telescopes are very commonly used. Various space agencies, including NASA have employed many reflecting telescopes and they are very popular among amateur telescope buyers.

Newton’s Law of Cooling

This theory provides an empirical formula for calculating the rates of cooling. The law states that the rate of cooling of a body is directly proportional to the temperature difference between the body and its surroundings.

This can be used to find the rate of cooling of objects or how long it will take to reach a certain temperature.

You could for instance calculate the temperature of a cup of tea. Or how long it would take an ice cube to melt given its initial temperature.

If finding the temperature of cups of tea or figuring out how long it takes to melt ice do not sound very important, then the Law of Cooling has many other more interesting and important applications.

For instance, it has been used in forensics in estimating the time of death of a body some time after death. It is used to help maximize the efficiency of designs of heating/cooling systems such as solar heating systems. And many other things where it is important to understand changing temperatures over time.

This too involves elements of calculus and is yet another example of the myriad uses of calculus. And the kind of relationship you can discover using calculus and some careful reasoning.

older Newton
Here is an older Newton.

The “Perfect Coin”

Newton was Warden of the England’s Royal Mint and was thus responsible for trying to minimize the counterfeiting of English coins.

Counterfeiting was a major problem. In the late 1600’s, England’s financial system was in dire trouble. England’s’ currency was composed of silver coins. The coins value was often worth more than the assigned value of the coins.

This led to people melting down or clipping silver from the edges to sell to France. As a result, many of the remaining coins were a badly damaged mass of unrecognizable silver chunks. Which was good news for counterfeiters, as it made it very easy to pass off some very non-coin like objects as coins.

So what did Newton do to solve this problem?

He went undercover, investigated, and apprehended the counterfeiters himself. This drew him to many different corners of Britain in his zeal to stamp out the illegal activity. So, basically, Newton when out and acted as a kind of Batman, investigating and apprehending counterfeiters.

Armed with a good understanding of all this counterfeiting activity, he recalled all the coins and had them melted down and reforged into a new design.

This was a pretty bold move, considering the entire country had to go without coins for an entire year. The result was a higher-quality coin with a harder to counterfeit design.

How did this work? Well, the coins you have in your country likely have those grooves/ridges on them that many coins in many countries have. Newton introduced this so that that it was impossible to mill the coin without it being detected. Thus greatly reducing the counterfeiting of silver coins.

A simple thing, but very effective.

Editor’s Note: To read more about Newton’s detective career (!), you can check out this book:

Newton and the Counterfeiter
Buy from Amazon


Alright, that covers most of his more interesting or significant contributions to science and one more interesting contribution to justice. As mentioned at the start, this is not an exhaustive list, but a brief overview of his considerable contributions.

How might one sum them up? Well, he created one of the most important mathematical techniques yet created, calculus. He helped prove the immense power of induction combined with mathematical reasoning. And how these can help one discover a great deal about the world around them.

He helped create physics as a true science. Before him, physics, as a field of study of the fundamental nature of reality, conducted through experimentation and reason, was largely non-existent. He helped show the universal power of what would come to be known as the scientific method and helped usher in physics qua science.

His scientific contributions, especially in the field of mathematics, mechanics and optics were immense. Enough to make him one of the greatest scientists ever.

But, I think his greatest legacy was his philosophical legacy and the impact he had on the world. How his work helped transform the world and do so much to create physics as we know it is today. Or at least, as it was known until the late 19th century.

His philosophical legacy can hardly be understated. But, we are not here to discuss that at any great length today. That will be the topic of a future episode.

Newton's Discovery of the Refraction of Light
Newton’s Discovery of the Refraction of Light, by Pelagio Palagi.


But, that brings us to the end of this episode. I hope you enjoyed our brief coverage of the great scientific works of Sir Isaac Newton.

Remember to check out the website and subscribe if you like our podcast, sign up to our mailing list or follow us on Facebook or Twitter to get the updates!

You can also make a donation to the show, which allows you to access our extra member-only content.

You can also look at our Metaphysics of Physics merchandise, if you wish. All profits from these go back into the show.

Any amount contributed is received with appreciation and goes towards time and resources spent on producing and promoting the show!

More information on either of these can be found on our website.

You can find out more about our donation subscription plan here.

Our Metaphysics of Physics merchandise can be found here.

You are welcome to send in questions about any of the things talked about in this episode or about irrational stuff in physics or the philosophy of science in general. Send them to

Thanks for listening! Please tune in for the next episode and start thinking of some questions! Until then, stay rational!

Leave a Reply

Your email address will not be published. Required fields are marked *