The Doctor and the Rough Rider by Mike Resnick

does the other genius think?”
    “I think we're working in the dark here,” replied Edison. “The unhappy truth is that
     someone's going to have to see this War Bonnet in person before we can create a weapon
     that will work against him, and even that probably won't be enough.”
    “Why the hell not?” persisted Holliday.
    “Pretend he's standing right over there, by the door, and that the ceiling is high
     enough to accommodate him,” said Edison, getting up, walking to the door, and turning
     to face them. “He's here to kill you. Ned's already talked about some of the problems
     of defending yourself, but let's concentrate not on that but on killing, or at least
     neutralizing, War Bonnet. Okay, Doc, you draw your gun and fire six quick shots. Either
     they bounce off him, or he absorbs them with no ill effects. Now what do you do?”
    “Run like hell,” said Masterson, only half-kidding.
    “Well, right at the moment, so would I,” said Edison, returning his smile. “And that's
     why we need to know more about him.”
    “For example?” asked Roosevelt.
    “If Doc shoots you in a vital spot, you'll die—and if you shoot him, he'll die. That means you each have the same physical weaknesses. Is that true of War Bonnet?
     Which is to say, it seems obvious that those fiery hands of his are meant to burn
     you, either at close quarters, as when he grabs you, or at a distance, if he has some
     mechanism whereby he can aim and release that fire. So the obvious question is: Is
     he himself susceptible to fire, or at least to heat? If he is, I can create a carbon
     arc projector that I guarantee will throw more heat at him than he can throw at you…but
     will that harm, or even bother him? I don't know.” Edison returned to his chair while
     considering his next line of approach. “All right, let's say that he's immune to fire
     and heat. It's a reasonable assumption, given that his arms and hands are made of
     flame. Will water put the fire out, or at least negate it to some degree?”
    “It seems reasonable,” agreed Masterson.
    “I see Theodore is shaking his head,” noted Edison with a smile. “Would you care to
     tell Bat why?”
    “I'd have to position myself next to a large source of water. This is not a small
     warrior, this War Bonnet, and those aren't small flames. And we don't know how hot
     the flames are. Could they turn the water to steam even before it hits them? Remember:
     he's a magical creature, so he doesn't necessarily obey all the laws of Tom's science.”
    “Absolutely right,” agreed Edison. He smiled again. “I would expect no less of a Harvard
     man.”
    “Let's concentrate on keeping the Harvard man alive,” said Holliday. “At least long
     enough for someone from Yale to come along and kill him.”
    Roosevelt uttered a hearty laugh. “Says the man who did not have the benefit of a
     New England education.”
    “Getting back to War Bonnet,” said Edison, “so far we've spoken about only heat, flame,
     and water. How about one of Doc's or Bat's bullets? I assume they won't bother him
     because of his magical origin, but until we know that for sure, we have to consider
     the possibility that the direct means of confronting and combating him may be the
     best. And there are factors that seem extraneous but may not be. For example, how's his endurance? Most huge men, well-muscled
     or otherwise, tire more easily than small, lithe men. What if you face him out in
     the desert, shoot his horse out from under him, and ride off?”
    “He won't be riding a horse, Tom,” said Buntline.
    “Are you quite sure, Ned?” retorted Edison. “If they can create War Bonnet, why can't
     they create a horse that stands sixty hands at the shoulder and weighs three tons?”
    “Damn!” muttered Buntline. “I never thought of that.”
    “Anyway, gentlemen, I could give you all the dozens of possibilitiesthat have occurred to me, but the end result would be the same: it's all guesswork,