The Mystery of Dialling.
Dialling is a science which few except experts understand now; the antiquary takes little note of it as he gazes upon the old dial plate and makes out the inscription upon it. The collector gladly buys the brass dial with its quaint lettering and division marks without even knowing where it came from, or what kind of stone column or pillar it originally capped. Yet there is far more interest in an old sundial installed in a modern garden amidst reconstructed old-world surroundings when the origin of the relic is known.
We have no record of the type of sundial referred to in Isaiah xxxviii, 8: "Behold, I will bring again the shadow of the degrees which is gone down on the sun-dial of Ahaz, ten degrees backward." There are, however, records of the sundial of the Chaldean astronomer Perosus, who lived about 340 B.C. It consisted of a hollow hemisphere placed with its rim horizontal, having a head or globule fixed so that as long as the sun shone above the horizon the shadow of the head fell on the inside of the hemisphere.
In more recent days the making and fixing of the dial with its gnomon was carried out on fixed principles, and there is now no difficulty about such an installation provided that the same astronomical conditions are observed. (For rules governing dialling, see [Glossary].)
FIG. 83.—EARLY DIALS—ON THE LEFT AN ARMILLARY DIAL; IN THE CENTRE PILLAR DIAL; AND ON THE RIGHT A RING DIAL.
(In the British Museum.)
FIG. 84.—CURIOUS OLD MICROSCOPE, MADE IN 1780.
(In the Municipal Museum, Hull.)