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张衡出于史官的职守,也常借地动来发表“政善则休祥降,政恶则咎征见”的言论,但他在太史令任上,研究而创制出地动仪,又显然与当时的神学观针锋相对,其阻力之大可以想象。朝廷上下都将极力排挤张衡。直到138年,地动仪证实了陇西的大地动后,众人“于是皆服其妙”,“自此以后,乃令史官记地动所从方起”。
张衡公元78年出生在河南的南阳。他的祖父曾经官至太守,显赫一时,但是到张衡这一代,已经家道中落。清苦的家境使张衡能够潜下心来做学问。少年时代的张衡饱读诗书,从16岁起,他走出家乡,游历名山大川、古城巷陌,开阔了自己的视野,也了解了民众的疾苦。
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演示昼夜更替及其原因
以电灯或一只电代表太阳,使之与地球仪的球仪心在同一平面上.地球仪绕地轴(地轴北端指向正北方)自西向东转动。地球自转的周期(转一周3600)为一个恒星日,即23小时56分4秒。地球仪自西向东自转时,在北极上空看地球仪呈反时针方向旋转;从南极上空看地球仪呈顺时针方向旋转;从赤道上空看地球仪自西向东旋转,这三种表述是一致的。由于地球(仪)是一个不透明的球体,同一时间太阳(电灯或手电)只能照亮地球的一半,即向日为昼,背日为夜。被太阳(电灯或)照亮的半球,称为昼半球,半夜照亮的半球,称夜半球。向个斗球之间的分界线(两条)合为一个圆圈,叫晨昏线(圈)。地球(仪)不停地自西
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