What Is a Hydroscope?

A hydroscope is one of several instruments that combines the electronic or optical analysis of physical properties with water. In ancient times, this referred to a water clock, which measured a trickle of water from a graduated tube. It also meant a kind of nautical telescope that was aimed downward, for observation and projection of underwater images to a screen. In contemporary contexts, a hydroscope refers to a benchtop piece of laboratory equipment that measures the presence and qualities of water, ink balances, and emulsification traits. This equipment might resemble a box with sensors and electronic readout interface.

The original hydrometer, or hydroscope, was invented by Hypatia of Alexandria, a fourth-century Greek scholar and scientist-philosopher. A mathematician, Hypatia was concerned with finding liquids' specific gravity; ancient designs consisted of a glass stem and mercury or lead-weighted bulb. The heavier the density, the lower the float would sink.

This stem was marked with units of measure to permit a direct reading of a liquid's specific gravity. The buoyancy of a solid relates to the displacement of fluid, so the greater the density, the more the hydrometer would sink. Modern hydrometer designs may measure specific liquids containing alcohol, lactose, saccharin, and more.

One nautical variety of hydroscope consists of a long tube housing an arrangement of optical lenses, similar to a telescope. This tube extended from a ship to below the surface of the water. Light reflected from submarine objects into the hydroscope, which also magnified the scene. Images were then projected onto a screen for direct observation from the deck. The practice permitted ancient sailors to observe objects beneath the waters, such as marine life, signs of military activity, or salvage.

Today's laboratory hydroscope allows researchers to observe many liquid variables. These can include emulsification, or phasing of multiple liquids, saturation points, and viscosities. Additional variables can include tack, or how an ink fixes; torque, which relates with flow and resistance; and the mixing effects of different inks. In other words, a hydroscope may allow an operator to predict how a lithographic ink may perform when applied to a press.

Applications of hydroscopy typically include emulsification tests for ink/water balances for printing presses. This permits the analysis or development of inks and other process specifications. Generally, hydroscope designs may serve to make clear observations of a fluid medium; others may also serve to detect the presence of water in air. The many ways to study liquids may be reflected in the words of Hypatia: "Truth is a point of view, and so is changeable."