I estimated the effect of Mercury's northerly declination (different of course for a vertical wall, than for the cross-rod in fig.

8, which, in fact, agrees with a declination-circle), and found that he would pass out opposite a particular point of the wall a certain time after the sun.

I then turned the telescope towards that point, and focussed for distinct vision of distant objects, so that the outline of the house was seen out of focus.
As the calculated time of apparition approached, I moved the telescope up and down so that the field swept the neighbourhood of the estimated point of apparition.

I need hardly say that Mercury did not appear exactly at the assigned point, nor did I see him make his first appearance; but I picked him up so soon after emergence that the outline of the house was in the field of view with him.

He appeared as a half-disc.