The narrator keeps flitting between fear and curiosity – he is "a battleground" between these two feelings – but eventually, his curiosity wins and he goes to find a better view of the pit. Although it's getting dark now, which is not the best time of day to examine Martians, especially in a chapter titled "The Heat-Ray." (Although perhaps the narrator can be forgiven for missing the clue of the chapter title since this is the first appearance of the phrase "Heat-Ray" according to the Oxford English Dictionary.)
Many of the other people are also bucking up and returning to the pit. Some of these people (fools?) walk really close to the cylinder, waving a white flag to signal their peaceful intentions.
Later, the narrator learns that Ogilvy, Henderson, and Stent were in this group. (If you ever find yourself making contact with aliens, please don't assume that they will know that a white flag means "we come in peace." It's very possible that on Mars, a white flag means "Your mom.")
There's a flash of light in the pit and some bright green smoke. As the people get closer to the pit, a dome-like object rises out of the pit and…
Nowadays, we have lasers and flamethrowers, so this might not sound so amazing to us, but imagine reading this in 1898: "It was as if some invisible jet impinged upon them and flashed into white flame. It was as if each man were suddenly and momentarily turned to fire" (1.5.14).
The narrator is so shocked by this that he doesn't realize that people are dying. "All I felt was that it was something very strange" (1.5.16). He is so shocked that he doesn't move and would've died, but the Heat-Ray happens to miss him.
Eventually he realizes his situation – aliens are shooting a Heat-Ray at him – so he decides skedaddle. He runs, weeping silently like a child (his words, not ours – none of the children we know weep silently, but maybe things were different in the 1890s).