eg. 44' 8" N. gives us Mercury's place, which it appears is
rather less than 1-3/4 degree north of the sun. Thus, about 1h. 42m.
after the sun has passed the cross-rod, Mercury will pass it between the
first and second divisions above the point of fastening. The sun will
have set about an hour, and Mercury will be easily found when the
telescope is directed towards the place indicated.

It will be noticed that this method does not require the time to be
exactly known. All we have to do is to note the moment at which the sun
passes the point of fastening of the two rods, and to take our 1h. 42m.
from that moment.

This method, it may be noticed in passing, may be applied to give
naked-eye observations of Mercury at proper seasons (given in the
almanac). By a little ingenuity it may be applied as well to morning as
to evening observations, the sun's passage of the cross-rod being taken
on one morning and Mercury's on the next, so many minutes _before_ the
hour of the first observation. In this way several views of Mercury may
be obtained during the year.

Such methods may appear very insignificant to the systematic observer
with the equatorial, but that they are effective I can assert from my
own experience. 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. 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