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Lucretius in De rerum natura, book 6 verses 310 tries to explain the nature of lightning. Apparently he says that a body moving quickly through the air acquires some heat.

The Latin verse is:

non alia longe ratione ac plumbea saepe fervida fit glans in cursu, cum multa rigoris corpora dimittens ignem concepit in auris.

English translation

And when, swift-winged, the ball of missle lead Heats, by degree its gross unkindled parts Losing, and fires by atoms gained from air

Also lines 182-183 of Book VI:

Melted, as melt the missile balls, at times Of lead shot rapid.

Lucretius wrote in 1-st century BC. What kind of "missile leads" could fly at that time with such velocity that they could be appreciably heated by air? Heated so much that they are melted??

Edit. Let us make a simple calculation. Specific heat capacity of lead is 0.13, J/(g.K) (from Wikipedia). So to heat a 100 g lead bullet by 10 degrees one needs the energy of 130 J, or about 13 Kilogram-force.meters. A slinger probably cannot transfer much more energy to a projectile. And it does not matter how this energy is converted to heat: by air friction or by the impact. Very far from "melting lead".

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    Meteorites have been known since ancient times, and are hot when they land. That and knowledge of frictional heating in general seems sufficient explanation for the observation.
    – Pieter Geerkens
    Commented Sep 6, 2020 at 16:11
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    It is strange to describe a meteorite as a lead missle. And it is strange to assume that Lucretius speaks of meteorites here.
    – Alex
    Commented Sep 6, 2020 at 16:25
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    The Latin word used, "glans", is translated traditionally as (1) "acorn"; (2) "beechnut"; or (3) "bullet thrown from a sling". Part of the translation issue is to translate what is a metaphor in Latin into English where exact words exist for the various meatphorical uses in Latin - but the best exact choice is unclear.
    – Pieter Geerkens
    Commented Sep 6, 2020 at 17:04
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    @justCal Or perhaps he was just calling it a "flying rock" (ie "bullet thrown from a sling").
    – Greg
    Commented Sep 8, 2020 at 9:30
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    Is it likely that Lucretius (or his sources) distinguished air heating (which would be negligible for the lead projectile) with the heating caused by deformation when it hits something (which might not be)? They weren't stupid by any means, but even the smartest and best-educated had trouble distinguishing fact from fancy in the natural world. I can easily see them assuming that air -- being as an element hot and wet -- might have what heated the lead rather than what it hit.
    – Mark Olson
    Commented Sep 9, 2020 at 13:13

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My guess (and we can really do little more than guess) is that he means lead slingstones. John Reid of the Trimontium Trust did experiments indicating lead shot from a hand-sling can be loosed at about 100mph by experianced slingers. So not only would they deform on impact, but they'd probably be a little warm after. I don't have the math or the physics to tell you for sure, but certainly when I hit some lead with a hammer repeatedly or with sufficient force it feel warmer in my hand.

If that holds true it doesn't seem a great stretch, if a lead shot is warm after hitting stone or armor, that something moving even faster would be hotter. (from Lucretius' point of view anyway)

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    Guesswork is not really what we look for on this site. Hitting something with a hammer is not at all similar to the friction of flying through the air - and I fully expect the ancients understood that.
    – Pieter Geerkens
    Commented Sep 8, 2020 at 16:20
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    I can swing a hammer at far below 100mph, and yet cause a piece of lead about the same size as roman shot to heat up. Stating "my guess" was directed at his actual meaning, which barring Lucretius rising from the dead can't be known with 100% accuracy. My math/physics admission was likewise an admission that, while I can't run the specific numbers for you, similar energy transference indicates it would be heated to some extent.
    – Dario Quint
    Commented Sep 8, 2020 at 16:31
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    @DarioQuint - please add that comment to the answer - and if you can cite the Trimontium Trust paper, that will help (I tried, but there are multiple papers to which that could refer).
    – MCW ♦
    Commented Sep 8, 2020 at 16:48
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    When I drive my car at 100mph its extrerior surface is not appreciably heated, not even mentioning the melting point of lead:-)
    – Alex
    Commented Sep 9, 2020 at 22:32
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    @Alex: I think the point here is that Lucretius was mistaken about the source of the heat. It wasn't from the friction of flying through the air, but from deforming on impact.
    – jamesqf
    Commented Feb 7, 2021 at 4:43

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