The conclusion drawn from the religions of Egypt and Chaldæa, as to the existence of a very long period of advanced civilization prior to the historical era, is fully confirmed by the state of the arts and sciences at the commencement of the earliest records. A knowledge of astronomy implies a long series of observations and a certain amount of mathematical calculation. The construction of great works of hydraulic engineering, and of such buildings as temples and pyramids, also proves an advanced state of scientific knowledge. Such a building, for instance, as the Great Pyramid must have required a considerable acquaintance with geometry, and with the effects of strains and pressures; and the same is true of the early temples and ziggurats, or temple observatories of Chaldæa. There must have been regular schools of astronomers and architects, and books treating on scientific subjects, before such structures could have been possible. The knowledge of science possessed by a nation affords a more definite test of its antecedent civilization than its religion. It is always possible to say that advanced religious ideas may have been derived from some supernatural revelation, but in the case of the exact sciences, such as arithmetic, geometry, and astronomy, this is no longer possible, and their progress can be traced step by step by the development of human reason. Thus there are savage races, like the Australians at the present day, who cannot count beyond "one, two, and a great number"; and some philologists tell us that traces of this state can be discovered in the origin of civilized languages, from the prevalence of dual forms which seem to have preceded those of the plural.