“潮程”试析

An Attempt to Analyze the Method of Measuring with Tides

在充分掌握潮汐规律之后,南宋以后的浙江、福建沿海方志中出现了以"潮次"与"潮数"记载港湾及岛屿间距的现象。通过梳理和解读有关方志及海防图,笔者发现在福建首先出现以"潮次"划分潮区的现象,在浙江则用"潮数"来估算岛屿间的距离。本文将这种用潮汐时刻结合航海以估算海道距离的方式称作"潮程"。潮数可分解作半潮、一潮、二潮等,且潮数有潮数值,各潮数的数值差异较大。再将潮数与更数比较,发现两者之间虽计时方式不同,但都被用作海道的计程单位。不同的是,潮数用来注记近岸岛屿间距,更数则用来表述长距离的海道。

Coastal Zhejiang and Fujian began to estimate distances according to the timing of tides after the Southern Song period.Local gazetteers and coastal defense maps reveal that the frequency of tides(chaoci)was first used to differentiate tidal zones in Fujian,while the number of tides in a day(chaoshu)determined the distance between islands in Zhejiang.Each unit of measurement involves a tidal value,such as"half tide","one tide",and"two tides,"although these units vary widely among one another.Tidal measurements(chaoshu),like geng,calculated distances of sea passages according to the passage of time.However,tidal measurements was used to measure the distance between off-shore islands,while geng was used to measure long-distance sea journeys.