: The temperature you exist in isn't the same
: temperature as your watch sees. If you wrist
: actually got to -22C it would be frozen
: solid and it would turn black and die. It's
: doubtful if your watch ever gets below
: freezing on your wrist at all. Same for
: heat. Resting skin temperature is 31 C, and
: if it gets hotter than that your body tries
: to remove the heat by sweating or moving the
: blood around. If your body temperature
: exceeds 41 degrees C you die.
: My Speedmaster Mark II survived 20 Minnesota
: winters (down to -40C) and twenty summers up
: to 40C, and I rarely took it off except at
: night. It finally succumbed to incompetent
: watch repair more than it did to the
: climate.
: BTW, the thermal expansion coefficient for
: GLASS is WAY larger than quartz or sapphire.
: Same for titanium over steel. That's why the
: SR-71 Blackbird was made out of titanium
: instead of steel, and why my semaster is Ti
: also.
Actually, the skin on supersonic aircraft is titanium because the higher melting point of Ti over Al gives it better creep resisitance ( resistance to softening under constant load). This is potentially an issue whenever you exceed about .5 of the melting temp in absolute degrees. In any case, the skin on supersonic aircraft gets quite hot as a result of "friction" with the air at extreme speeds. It is quite remarkable how hot it can be. I recall flying on the Concorde and noticing that the window felt hot at the 1500 mph or so. If the speed gets high enough, negligible friction is not all that negligible even in cold high altitute conditions.
