Physics of cold starts

[kerry]

I've been starting 617's in cold weather for about 7 years now. I (and others on this forum) have noticed that in very cold conditions, the first starting attempt is always the best chance to get the engine going. Any subsequent attempts to start the engine, even if glowed as long as the initial attempt, are more difficult. Why is this the case? It almost seems as if subsequent attempts after the first are only successful once the heat from turning the engine over is enough to ignite the fuel. In other words, the glow plugs seem less effective in the later start attempts?
These thoughts are spurred by the fact that I started the 116 at 5 degrees this morning without pluggin it in after replacing a glow plug on Friday just to see if the glow system was working correctly again. I glowed for 75 seconds and engine fired after about 3 or 4 revolutions but I foolishly let off the starter before it was running steadily enough and it stopped. The next attempt, even with a 75 second glow and the engine previously running momentarily, took a good 30 seconds of cranking before a single cylinder fired and then another 15 seconds of cranking before enough cylinders were firing to keep it running.

Any good explanations out there?