"When about midway during the prayer, there was a glorious sensation passed through the house; and we, having our heads bowed in prayer, felt a sensation very elevating to the soul. At the close of the prayer, F. G. Williams being in the upper east stand- -Joseph being in the speaking stand next below--rose and testified that midway during the prayer an holy angel came and seated himself in the stand. When the afternoon meeting assembled, Joseph, feeling very much elated, arose the first thing and said the personage who had appeared in the morning was the Angel Peter come to accept the dedication."
This is an excerpt from Truman Angell's autobiography, recollecting the dedication ceremony for the Kirtland Temple. I remember hearing in Sunday School the stories of angels at the dedication, but I only came across this passage today.
According to Angell, no one actually SAW anything: it was Smith, after the alleged fact, who tried to tell everyone there was TOTALLY an angel there, he was RIGHT THERE, and, oh yeah--it was PETER! But none of you dopes saw him because your heads were bowed during the prayer. Swear to God.