12 August 2005

Don't believe Jules Verne on a hot day

Cyrus Harding1, dipping in his hand, felt the water oily to the touch. He tasted it and found it rather sweet. As to its temperature, that he estimated at ninety-five degrees Fahrenheit2. Herbert having asked on what he based this calculation,―

[sic]3 quite simple, my boy," said he, "for, in plunging my hand into the water, I felt no sensation either of heat or cold. Therefore it has the same temperature as the human body, which is about ninety-five degrees."
Jules Verne, The Mysterious Island

The National Weather Service is predicting that today the air temperature will go up to about 36° C (96° F) around Washington, DC. So, by Jules Verne's logic, it should feel just right and quite comfortable outside. Which is, of course, total nonsense.

Thermodynamically, no chemical process can be 100% efficient. As a result, all metabolic activities produce heat, which is what humans and all other animals use to warm up their bodies. However, because humans cannot turn off their metabolism, heat is always generated and the excess must be dissipated to the surroundings to prevent the body from overheating above the normal temperature of about 36.7° C.

Whenever a body is at a higher temperature than its surroundings, the rate at which energy is lost to the surroundings in the form of heat is proportional to the temperature difference between the body and the surroundings. In other words, as the temperature of the body approaches that of the surroundings, less and less heat is transferred to the surroundings. And that is why when the ambient temperature is near the normal body temperature, rather than feel comfortable, we feel hot, because our bodies begin to overheat.

The situation is slightly different in water, because water is more efficient than air in conducting heat. That is why being in water at 36° C feels more comfortable than being in air at 36° C. Nevertheless, when you put your hand in water at 36° C it feels warm. Believe me, because I tried it last night. I filled up a sink with water while adjusting the temperature to about 36° C by turning the hot and cold water faucets on and off. When I put my hand in it, it felt warm, not "neutral". My wife, who voluntereed as an unbiased subject (she didn't know what the temperature was), also reported that the water was warm.

I can't forgive Verne for not having the common sense to test his idea before putting it in his book. Maybe he didn't have a thermometer.

1. Some editions, for example the French text at Gutenberg, give this name as Cyrus Smith.
2. The French text gives the temperature as “quatre-vingt-quinze degrés Fahrenheit (35 degrés centigrades au-dessus de zéro)”.
3. It should, of course, be “It’s”. This simple error is present both in my paperback copy and in the Gutenberg e-text.


deniz said...

Interesting! Makes me wish I lived under water instead of in my non-air-conditioned sticky muggy apartment!

Tim Pearce said...

So, at what temperature would the water be imperceptible? The imperceptible temperature must have to do not only with the actual temperature of the water, but also with the difference in temperature from that in which your hand was before you immersed it. For example, try the following experiment. Get three drinking glasses in a row. In one, put cold water, in the middle, put room temperature water, and in the other, put warm water. Put one finger of one hand in the cold glass and a finger from your other hand in the warm glass for about a minute. Then put both of those fingers into the same middle glass. To the finger from the cold glass, the water will feel warm, and to the finger from the warm glass, the water will feel cool.

In sensory deprivation experiments, in addition to having all light and sound blocked, subjects are often suspended in water to remove as much touch sense as possible. I wonder what temperature the researchers use for that water, because they don't want subjects to feel either hot or cold.

Still, I wonder what combination of temperature and other circumstances will cause water temperature to feel no different than where the hand had been.


"Makes me wish I lived under water..."

She'd like to be
under the sea,
in an octopus's garden,
in the shade.


"I wonder what temperature the researchers use for that water, because they don't want subjects to feel either hot or cold."

The water in a swimming pool always feels warmer when you are moving around than it does when you are just standing, because in the latter case your body has less excess heat to dissipate and instead your core temperature starts to go down. So I suspect in a sensory deprivation pool the water temperature is probably just below 36 C, because the person is just laying there.


One company(www.floattank.com/what.html) says the water in their floatation tanks is "kept at a constant 34.5 degrees Celsius - relaxed skin temperature. As a result, the nerve endings which cover the surface of the skin no longer perceive any sense of separation between the skin and the silky mineral solution which surrounds it."

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