Tidal Information by Ball Signal

The maritime ball signal was a model for some early railway signals, notably in the U. S. and Germany

Many harbours had an alluvial deposit at their entrances, a bar, that could only be crossed by ships at sufficiently high stages of the tide. The depth of water over the bar could not be easily determined by observation, nor predicted accurately enough from tide tables. A ship had to feel its way with a sounding line, something very hazardous with a sailing ship that lacked mobility and could easily be blown aground. It was usually important to dock as promptly as possible for business reasons, so knowing when a port could safely be entered was of economic importance. Ships of different sizes and loading required different minimum depths of water, so knowing the actual depth was desirable.

To eliminate this problem, port officials would have the depth of water constantly monitored with a sounding line or height gauge, and would signal the state of the tide to ships by means of an optical telegraph on some prominent height, where it could easily be seen from ships in the offing. This telegraph consisted of a mast and yardarm, on which light balls and flags could be displayed. The balls were seen black against the sky background, however they were painted. One system was as follows. A ball hoisted to the crossing of mast and yard signified that there was 3 metres depth of water. For each ball hoisted below this ball, there was an additional metre of depth. For each ball hoisted above the central ball, there was an additional two metres of depth. A ball hoisted at the left end of the yard added a quarter metre, and a ball at the right end a half metre, additional. In this way, water depths from 3 to 8-3/4 metres could be displayed with only six balls. The figure shows the display for 4-1/2 metres depth. At night, a coloured light was hoisted to the crossing of the mast and yard, and white lights were hoisted for the other balls, as necessary.

Another, simpler, system used a white flag with a black cross, and a black triangular pennant. The flag was hoisted when there was 2 metres of water, with the pennant above it if the tide was flowing, and below it if the tide was ebbing. At high tide, the flag was shown alone. A red flag hoisted at the mast indicated that ships could not enter the port.

The ball signal was adapted as a railway signal, especially in the United States, before the introduction of semaphore signals in the 1870s. When used as a station signal, a raised ball gave permission to enter or leave the station. This gave rise to the term highball for a hand signal to proceed, which is still used, although ball signals were actually quite rare and not generally used, except in New England. They were predominantly used at drawbridges, crossings and junctions, where a raised ball was the signal of safety. At junctions and level crossings, different routes were distinguished by different numbers of balls, shape or painting of the balls, or balls at different locations. In at least one case, a lantern was placed within a ball by night, and shone through a transparent window. Usually, lanterns were hung beneath the balls as a night signal. The last ball signal governed a crossing at Whitefield, New Hampshire, and was still in service in 1965.

From published rules and regulations, it was gathered that the Great Western Railway briefly used ball signals as station signals, in one or two places, before the disc and crossbar signal was adopted for this purpose. This is plausible, but firm evidence is still required. That the word "ball" could have been used for "disc" is very unlikely, and even disc signals were not widespread at the time.


A.-L. Ternant, trans. R. Routledge, The Telegraph (London: G. Routledge and Sons, Ltd., 1895)

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Composed by J. B. Calvert
Created 6 May 2000
Last revised 6 May 2000