It may have been the astronomical knowledge of the Chaldaeans which gave them the confidence to adventure on important voyages.  Scripture tells us of the later people, that “their cry was in the ships;” and the early inscriptions not only make frequent mention of the “ships of Ur,” but by connecting these vessels with those of Ethiopia seem to imply that they were navigated to considerable distances.  Unfortunately we possess no materials from which to form any idea either of the make and character of the Chaldaean vessels, or of the nature of the trade in which they were employed.  We may perhaps assume that at first they were either canoes hollowed out of a palm-trunk, or reed fabrics made water-tight by a coating of bitumen.  The Chaldaea trading operations lay no doubt, chiefly in the Persian Gulf; but it is quite possible that even in very early times they were not confined to this sheltered basin.  The gold, which was so lavishly used in decoration, could only have been obtained in the necessary quantities from Africa or India; and it is therefore probable that one, if not both, of these countries was visited by the Chaldaean traders.

Astronomical investigations could not be conducted without a fair proficiency in the science of numbers.  It would be reasonable to conclude, from the admitted character of the Chaldaeans as astronomers, that they were familiar with most arithmetical processes, even had we no evidence upon the subject.  Evidence, however, to a certain extent, does exist.  On a tablet found at Senkareh, and belonging probably to an early period, a table of squares is given, correctly calculated from one to sixty.  The system of notation, which is here used, is very curious.  Berosus informs us that, in their computations of time, the Chaldaeans employed an alternate sexagesimal and decimal notation, reckoning the years by the soss, the ner, and the sar—­the soss being a term of 60 years, the ner one of 600, and the sar one of 3600 (or 60 sosses).  It appears from the Senkareh monument, that they occasionally pursued the same practice in mere numerical calculations, as will be evident from the illustration. [PLATE XVIII., Figs. 1, 2.]

[Illustration:  PLATE 18]

In Arabic numerals this table may be expressed as follows: 

[Illustration:  PAGE 66]

The calculation is in every case correct; and the notation is by means of two signs—­the simple wedge [—­] , and the arrowhead [—­] ; the wedge representing the unit, the soss (60), and the sar (3600), while the arrowhead expresses the decades of each series, or the numbers 10 and 600.  The notation is cumbrous, but scarcely more so than that of the Romans.  It would be awkward to use, from the paucity in the number of signs, which could scarcely fail to give rise to confusion,—­more especially as it does not appear that there was any way of expressing a cipher.  It is not probable that at any time it was the notation in ordinary use.  Numbers were commonly expressed in a manner not unlike the Roman, as will be seen by the subjoined table. [PLATE XVIII., Fig. 3.] One, ten, a hundred, and a thousand, had distinct signs.  Fifty had the same sign as the unit—­a simple wedge.  The other numbers were composed from these elements.