H. M. Greenwich Mean Time 10 30 Difference of Longitude, _deduct_ 0 6 —— —— Local Mean Time 10 24 Difference of Equation, _add_ 0 10 —— —— Andover Solar Time 10 34 —— —— So we see that on 1st October the dial must be fixed 4 minutes faster than the watch. The gnomon of a horizontal sundial is always fixed on the XII. o’clock line, which represents the _true_ north and south meridian, and its edge is elevated above the plane to an angle equal to the latitude of the place. In the northern hemisphere XII. o’clock and the elevated end of the gnomon are always placed towards the north, but in the southern hemisphere the elevated end and XII. o’clock are placed facing the south. In northern latitudes the sun is always _due south_ at XII. o’clock by the sundial throughout the year, and in southern latitudes it is always _due north_ at XII. In both hemispheres the sun is always due east at VI. a.m. and due west at VI. p.m. Sundials can be fixed in dull weather, but a magnetic compass will then have to be employed; and although the fixing is simpler than when the sun is used the result is not so accurate. The directions are as given here:— Remove the studs and place the dial on the pedestal; take the compass, which should have a square box with needle, and lay it on the dial plate with the east or west side of the box close against the gnomon, and allow the needle to settle. Then, knowing the “magnetic variation” of the spot—for example, we will take London, which is 16° west of the _true north_—turn the sundial until the north end of the needle coincides with the 16° division west of the N. of compass dial. Take a pencil and mark the holes for studs; cut the holes and fill with grouting; place the dial on the pedestal and finally adjust with the compass before the cement sets. Sundials can be fixed by the compass, and by the sun, providing the sun is shining on the dial, at any time during the day. To read the time shown by a horizontal sundial, stand facing the sun, and for the morning hours take the right hand edge of the shadow, and for the afternoon hours take the left hand edge. Sundials of good make have the hour-lines and other divisions radiating from two centres, which are at a distance apart equal to the thickness of the gnomon, consequently there appears to be two hour lines at XII. o’clock, but really it is one, as the shadow at noon fills the space between the two lines. A sundial cannot be said to be complete without a motto of some description, and by inscribing one on the dial or pedestal it gives a fitting voice to the dignified dial.