722 THE KAMSDEN DIVIDING ENGINE. 



By receut Biblical critics* this dial is supposed to have been an obelisk, 

 whose shadow fell upou the steps of the palace of Ahaz, each step being 

 called a degree. 



It is by no means improbable however that these degrees were 

 marked on a plane of stone or metal. 



The simple records made by the Chaldean shepherds and herdsmen 

 of the observations by which they determined the seasons and by which 

 they were governed in the different operations of husbandry, led the 

 early cultivators of science to devise instruments (doubtless crude in the 

 beginning) by which they could obtain data for more accurately ascer- 

 taining the lengths of the solar and lunar periods. 



Astrology and astronomy bore the closest relationship to each other 

 at that remote period. 



"In the valley of the Euphrates there were in those days observa- 

 tories t in most of the large cities, and professional astronomers regu- 

 larly took observations of the heavens, copies of which were sent to 

 the king, as each movement or appearance in the heaven was supposed 

 to portend some evil or good to the kingdom." 



Among the first instruments of which there is record is the gnomon, | 

 with which the Babylonians were familiar, and from whom Herodotus 

 states (II, 109) " the Greeks learned the use of it, together with the 

 pole." The comparison of the perpendicular height of the gnomon, with 

 the length of its meridian shadow projected on a horizontal plane on 

 the days of the summer and winter solstices, afforded the early astron- 

 omer an opportunity to calculate the difference of the sun's meridian 

 altitudes on those days. 



ANCIENT ASTROLABES. 



Ptolemy, in his ''Almagest," written 145 A. d., describes an astrolabe 

 or circular instrument for making celestial observations (which he calls 

 aarpoXa'^ir.ov opyw^r^) which cousistcd of a heavy circle of metal arranged 

 so that when it was suspended the divisions which we now call 0° and 

 180° would come to rest in the same horizontal plane. 



A diametrical bar suspended in the center of the circle and turning 

 on a pin was furnished with disks containing slits through which any 

 heavenly body could be seen and its altitude determined in degrees or 

 parts thereof. 



Other astrolabes were constructed in early times, consisting of two 

 graduated circles set exactly at right angles. 



•Compare Isaiah ;?8: 8, revised version: " I will cause the sLadow on the steps, 

 which is gone down on the dial of Ahaz with the sun, to return backward ten steps, 

 80 the sun returned ten steps on the dial whereon it was gone down." 



t George Smith, "Assyrian Discoveries," p. 408. 



t Vitruvius, who wrote in the first century B. c, gives in Book i, chap. 6, direc- 

 tions for using the gnomon to ascertain the north and south line in laying out the 

 streets of a city, thus indicating that the Romans were not familiar with the magnetic 

 needle. ^ 



