Excerpt from the Fifth Edition

Next month, Russ Hobbie and I will receive the page proofs for the 5th edition of Intermediate Physics for Medicine and Biology. I welcome their arrival because I enjoy working on the book with Russ, but also I dread their coming because they will take over my life for weeks. The page proofs are our last chance to rid the book of errors; we will do our best.

I thought that you, dear readers, might like a preview of the 5th edition. We did not add any new chapters, but we did include several new sections such as this one on color vision.

14.15 Color Vision

The eye can detect color because there are three types of cones in the retina, each of which responds to a different wavelength of light (trichromate vision): red, green, and blue, the primary colors. However, the response curve for each type of cone is broad, and there is overlap between them (particularly the green and red cones). The eye responds to yellow light by activating both the red and green cones. Exactly the same response occurs if the eye sees a mixture of red and green light. Thus, we can say that red plus green equals yellow. Similarly, the color cyan corresponds to activation of both the green and blue cones, caused either by a monochromatic beam of cyan light or a mixture of green and blue light. The eye perceives the color magenta when the red and blue cones are activated but the green is not. Interestingly, no single wavelength of light can do this, so there is no such thing as a monochromatic beam of magenta light; it can only be produced my mixing red and blue. Mixing all three colors, red and green and blue, gives white light. Color printers are based on the colors yellow, cyan and magenta, because when we view the printed page, we are looking at the reflection after some light has been absorbed by the ink. For instance, if white light is incident on a page containing ink that absorbs blue light, the reflected light will contain red and green and therefore appear yellow. Human vision is trichromate, but other animals (such as the dog) have only two types of cones (dichromate vision), and still others have more than three types.

Some people suffer from colorblindness. The most common case is when the cones responding to green light are defective, so that red, yellow and green light all activate only the red receptor. Such persons are said to be red-green color blind: they cannot distinguish red, yellow and green, but they can distinguish red from blue.

As with pitch perception, the sensation of color involves both physics and physiology. For instance, one can stare at a blue screen until the cones responding to blue become fatigued, and then immediately stare at a white screen and see a yellow afterimage. Many other optical illusions with color are possible.

You may recognize parts of this excerpt as coming from a previous entry to this blog. In fact, we used the blog as a source of material for the new edition.

A Christmas Carol,
by Charles Dickens.

I will leave you with another excerpt, this one from the conclusion of A Christmas Carol. Every Christmas I read Dickens’s classic story about how three spirits transformed the miser Ebenezer Scrooge. It is my favorite book; I like it better than even IPMB!

I wish you all the happiest of holidays.

Scrooge was better than his word. He did it all, and infinitely more; and to Tiny Tim, who did not die, he was a second father. He became as good a friend, as good a master, and as good a man, as the good old city knew, or any other good old city, town, or borough, in the good old world. Some people laughed to see the alteration in him, but he let them laugh, and little heeded them; for he was wise enough to know that nothing ever happened on this globe, for good, at which some people did not have their fill of laughter in the outset; and knowing that such as these would be blind anyway, he thought it quite as well that they should wrinkle up their eyes in grins, as have the malady in less attractive forms. His own heart laughed: and that was quite enough for him.