Similar methods may be applied to determine from the position of a known object, that of any neighbouring unknown object even at night.

The cross-rod must be shifted (or else two cross-rods used) when the unknown _precedes_ the known object.

If two cross-rods are used, account must be taken of the gradual diminution in the length of a degree of right ascension as we leave the equator.
Even simpler methods carefully applied may serve to give a view of Mercury.

To show this, I may describe how I obtained my first view of this planet.

On June 1st, 1863, I noticed, that at five minutes past seven the sun, as seen from my study window, appeared from behind the gable-end of Mr.St.Aubyn's house at Stoke, Devon.