3 ms·

> 1643 when Evangelista Torricelli invented the mercury barometer iirc Tycho Brahe needed to make careful allowances for atmospheric refraction many decades be

> 1643 when Evangelista Torricelli invented the mercury barometer iirc Tycho Brahe needed to make careful allowances for atmospheric refraction many decades before this. Also iirc a rougher notion of this effect goes back to Ptolemy. I guess in thinking the following I'm just showing my lack of historical imagination, but: watching a sunset, and knowing it's at a distance many times the size of the earth, you'd think there must be something attenuating light which forms a layer much thinner than the size of the earth. This comports with a view of distant mountains vs. ones nearby, versus the sharp outline of the moon. You might still be very unsure whether this factor might include the air itself, and not just dust and vapor. If anyone wrote about this early on, I haven't heard of it.

teraflop 4y ago
You have to bear in mind that until the 17th century or so, the philosophical doctrine that "nature abhors a vacuum" seemed to be backed by very reasonable evidence: namely, the fact that it was basically impossible to actually create a vacuum through any technological means available. And until we had basic theories of gravity and the properties of gases, there was no theoretical justification for how a vacuum could form naturally. So it makes sense that to most thinkers of the time, it was more plausible for space to be completely filled with some kind of perfectly transparent but substantial aether. You raise a very interesting point, though. I would be very interested to learn what ancient philosophers thought about atmospheric haze. Did they recognize that the bluish appearance of distant mountains and the reddish appearance of sunrises/sunsets had a common cause? And if so, did they associate it with "air" as an elemental substance, or something else?
- flavius29663 4y ago
  > the fact that it was basically impossible to actually create a vacuum through any technological means available Do you have more sources on this? I would like to read up. As far as I'm concerned, vacuum is trivial to produce: by putting your palms together and then pulling them apart, by using blacksmith's bellows, and a lot of devices that used leather and/or bladders. I think the problem is in recognizing that you created vacuum, rather than creating it, so I would like to know if you have more insight into why you said that.
  - maweki 4y ago
    > by using blacksmith's bellows Creating a pressure differential where air flows in immediately. As vacuum seemingly cannot be sustained without constant work, it seems that nature does indeed not like vacuums. > vacuum is trivial to produce But not trivial to sustain. And it would be a sustained vacuum if it were between the earth and the moon or sun.
    - flavius29663 4y ago
      you can sustain it if it's properly sealed, but I see your point, people would have a hard time understanding why the outer space would apparently sustain such a large amount of vacuum. It seems unnatural to us, because we're so used to atmospheric pressure that we're taking it for granted.
      - seiferteric 4y ago
        I also thought of several examples; breathing in/out of a paper bag, hot air balloon, or that experiment where you put heat up or metal container and put the opening on water and it gets sucked in (or crushes a thin can). I can see that it takes work to sustain these, but what about just putting a glass bottle in your mouth and pulling a vacuum and carefully putting your thumb on top. You can create a slight vacuum in a glass bottle this way and it will stay there until you move your thumb and hear the "whoosh". But I guess it still "wants" to fill the void as soon as you unplug it, so I guess I understand.
        abecedarius 4y ago
        That kind of effect was studied and used in antiquity, as pneumatics. Aristotle's point of view did not hold sway everywhere or for all of that period; afaik pneumatics started with Empedocles and the clepsydra, and obviously the atomists favored the vacuum. I've kept out of this conversation because I'm too ignorant, but it seems worth saying that while "it doesn't fit with Aristotle's scheme of the world" may be a good enough explanation for most premodern western thinking, it's hardly all of it.

teraflop 4y ago

You have to bear in mind that until the 17th century or so, the philosophical doctrine that "nature abhors a vacuum" seemed to be backed by very reasonable evidence: namely, the fact that it was basically impossible to actually create a vacuum through any technological means available. And until we had basic theories of gravity and the properties of gases, there was no theoretical justification for how a vacuum could form naturally. So it makes sense that to most thinkers of the time, it was more plausible for space to be completely filled with some kind of perfectly transparent but substantial aether. You raise a very interesting point, though. I would be very interested to learn what ancient philosophers thought about atmospheric haze. Did they recognize that the bluish appearance of distant mountains and the reddish appearance of sunrises/sunsets had a common cause? And if so, did they associate it with "air" as an elemental substance, or something else?

flavius29663 4y ago
> the fact that it was basically impossible to actually create a vacuum through any technological means available Do you have more sources on this? I would like to read up. As far as I'm concerned, vacuum is trivial to produce: by putting your palms together and then pulling them apart, by using blacksmith's bellows, and a lot of devices that used leather and/or bladders. I think the problem is in recognizing that you created vacuum, rather than creating it, so I would like to know if you have more insight into why you said that.
- maweki 4y ago
  > by using blacksmith's bellows Creating a pressure differential where air flows in immediately. As vacuum seemingly cannot be sustained without constant work, it seems that nature does indeed not like vacuums. > vacuum is trivial to produce But not trivial to sustain. And it would be a sustained vacuum if it were between the earth and the moon or sun.
  - flavius29663 4y ago
    you can sustain it if it's properly sealed, but I see your point, people would have a hard time understanding why the outer space would apparently sustain such a large amount of vacuum. It seems unnatural to us, because we're so used to atmospheric pressure that we're taking it for granted.
    - seiferteric 4y ago
      I also thought of several examples; breathing in/out of a paper bag, hot air balloon, or that experiment where you put heat up or metal container and put the opening on water and it gets sucked in (or crushes a thin can). I can see that it takes work to sustain these, but what about just putting a glass bottle in your mouth and pulling a vacuum and carefully putting your thumb on top. You can create a slight vacuum in a glass bottle this way and it will stay there until you move your thumb and hear the "whoosh". But I guess it still "wants" to fill the void as soon as you unplug it, so I guess I understand.
      - abecedarius 4y ago
        That kind of effect was studied and used in antiquity, as pneumatics. Aristotle's point of view did not hold sway everywhere or for all of that period; afaik pneumatics started with Empedocles and the clepsydra, and obviously the atomists favored the vacuum. I've kept out of this conversation because I'm too ignorant, but it seems worth saying that while "it doesn't fit with Aristotle's scheme of the world" may be a good enough explanation for most premodern western thinking, it's hardly all of it.