The sundial, as already mentioned, shows _solar_ time, but by adding or deducting the differences, as shown above, _local mean time_ is found, and by again adding or deducting the difference of longitude, _Greenwich mean time_ is the result. For instance, a sundial at Wrexham (3° West longitude) on the 11th March indicates 11 o’clock, and we want to find Greenwich mean time. We proceed as follows:— H. M. Wrexham Sundial 11 0 Difference of Equation, _add_ 0 10 —— —— Local Mean Time 11 10 Difference of Longitude, _add_ 0 12 —— —— Greenwich Mean Time 11 22 —— —— We see by the above, that the watch should be 22 minutes faster than the dial. A well-made sundial should have engraved upon it an equation table and the longitude of the place where it is fixed, and the consequent allowance of time to be added or subtracted to find _Greenwich mean time_. =SUNDIALS SHOULD BE FIXED= on a bright, sunny day, a horizontal dial being fixed as follows:—First see that the stone pedestal on which the dial is to be fixed is perfectly rigid, also flat and level on top. Remove with a pair of pinchers or plyers the three button-headed studs that are usually fitted on the back of the dial, then place the dial approximately in position by moving it about until the shadows show the time within a few minutes, and with a pencil, mark the positions of the studs on the stone through the holes in the plate. Remove the dial and replace the studs in the dial; cut the three holes about twice as large as the heads, so that the dial has plenty of play to the right and left to facilitate final adjustment. Mix with water a little Portland cement, which is known as “grouting,” damp the holes in the stone and pour the grouting in and place the dial in its place, turning it until it shows correct _solar time_ of the place, taking care that the plate is level, and then allow the cement to set. The dial is now fixed, and requires no further refixing at any time. To ascertain correct _solar time_ for fixing purposes proceed as in the example given here, and for the purpose we will take Andover (1½° West) as the place where the dial is about to be fixed on 1st October.