206 
It is not known at what time this ancient time-keeper went out 
of fashion, but a water-clock was sent as a present to the 
Emperor Charlemagne by MHaroun-al-Raschid in the ninth 
century* (A.D. 807). 
The name Clepsydra, or Lose-Water, seems to have been 
succeeded by the Horologiwm, which also told the hour. This 
name was also given to the most ancient invention, the sun dial, 
and this, as we have seen, was originally a simple column, the 
shadow of which by its variations marked the hour. 
Aristophanes noted the hour of dinner by the shadow of his 
gnomon, called orovyeov, when it reached ten feet. 
Pliny tells us that the Emperor Augustus “converted an 
Egyptian Obelisk into a gigantic gnomon in front of his Mauso- 
leum in the Campus Martius.” 
This same Obelisk now serves the same purpose on the Monte 
Citorio at Rome. 
There were two kinds of sun dial used by the Ancients, the 
Concave and the Convex. The former was most usual. 
We are informed by Vitruvius that the Chaldeans invented the 
Concave, and Aristarchus, of Samos, the Convex, and also the 
Horizontal Dial. To Scopinus, of Syracuse, is assigned the 
invention of the Vertical, called Plinthus or Lacunar; one of them 
was set up in the Circus Flaminius at Rome. 
Theodorus invented one for all latitudes, and this, as Mr. King 
observes, implied an extraordinary proficiency in the science.t 
Having spoken of ancient classical dials and their inventors, we 
must now turn our attention to dials of the medizval period. 
A dial supposed to be of the Roman period was discovered at 
Dover, but the age is very uncertain, and it probably belongs to a 
much later date. A drawing of it is given in the Archzological 
Journal, vol. xxi., p. 262. 
* Eginheard Ann. Tranc. 
+ See Mr. King’s Paper in the Arch. Journal, vol xxi. 
