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"That made me think of Robert Service."

Robert Service had a rather rigorous rhythm to his work. Typically, anyone who thinks about him tends to keep him in mind for a while.

Anyway, back to Kilimanjaro. When you stand on Africa's burning savannah, looking up to the glaring whiteness atop Kilimanjaro, it must be a little daunting, as well as aggravating.

I mean, there you are, baking in the tropical sun, your breath whistling out of you with the sound and moisture content of a tea-kettle, and that mountain has the temerity to show you frigid whiteness that you cannot hope to reach.

What's going on with that?

Well, what's going on is called altitude. As you rise in altitude, the air gets thinner, and cooler. Even on a summer day, you can see this effect, as rising humidity finds a height at which its water vapor condenses into puffy white clouds.

It's very visibly obvious near Kilimanjaro, where the moisture content falls as snow.

This effect, the reduction of temperature, happens any time that air pressure is reduced. Let the air out of a tire, and you can feel instant coldness. (A coldness paid for when you compress the air in the first place, but let's not get distracted.)

This adiabatic cooling occurs even when the air involved isn't quite air as we think of it. It's a phenomenon of gases. It happens with oxygen, with nitrogen, and it happens with carbon dioxide.

At the present time, we know that the atmosphere of Venus is almost all carbon dioxide. So even though the surface temperature of Venus is hot enough to melt many metals, by simply rising in that very thick atmosphere, you will find cooler temperatures.

Unfortunately, even the highest mountains on Venus are not very high, and the temperature to start with is very, very high, (Venus is hotter than Mercury!)

But by a rather odd coincidence, that section of altitude where the temperature at last does drop into what we would consider more Earthlike normal, is also the section of altitude where the crushing pressure is more like that of Earth as well!

Where is this magical altitude? About thirty-five miles, or fifty kilometers, above that hellish surface temperature mentioned before.

Way far above any possible mountains.

I like to think of our sister planet as being like a "water-world" version of Earth, except that instead of water, Venus has an ocean of carbon dioxide. At the top of the ocean of carbon dioxide, at "sea-level" if you will allow the concept, the temperature, pressure, and the gravity, are all the most nearly Earthlike of any other place in our solar system, or within hundreds of light years of Earth.

So what good does that do us?

Another odd coincidence that works in our favor, is that in an atmosphere of carbon dioxide, all you need to do to find a lifting gas is find something lighter than carbon dioxide.

On Earth, lifting gases are limited to hydrogen, helium, and hot air.

On Venus, nearly everything that is a gas, is a lifting gas. Pure nitrogen, which is available in plenty in the oceans of carbon dioxide on Venus, (more than five times as much as on Earth!), is a lifting gas with half the power of helium on Earth.

Essentially, you could parachute into Venus atmosphere, inflate a balloon (or blimp) with nitrogen, and you could easily maintain that altitude as long as you wanted to.

Now, the only major difference between pure nitrogen, and regular air you can breathe, is the presence of twenty percent oxygen. So ordinary breathing air is a lifting gas on Venus.

If you had a semi-rigid structure, like a circus tent or a plastic greenhouse, all you'd have to do is fill it with breathable air and it would keep you afloat on that ocean of carbon dioxide. Fill it up with plants to keep turning carbon dioxide into oxygen and food, and you're a settler or colonist on another planet!