Know your Weather Instrument

Do you know your Barometer from your Hygrometer? How about your Thermometer from your Comfortmeter?

Here is a simple guide to help you decide on the most appropriate timepiece for your yacht or home, courtesy of Wempe Chronometerwerke.



The word “barometer” literally means “weight-measurer” or “pressure-measurer.” Barometers precisely measure atmospheric pressure. The oldest instrument designed to measure the pressure of the air is probably the so-called “weather glass.” Depending on the pressure of the atmosphere, the level of liquid would either rise or fall inside a specially crafted carafe with a long “beak.” At the beginning of the 17th century, G. de Donckere built such “weather glasses” in the Netherlands, where they were known as “thunder flasks.” Mariners relied on them to indicate impending changes in the weather. Modern barometers can reliably indicate weather trends 24 to 48 hours in advance.



A comfortmeter combines the advantages of a thermometer and a hygrometer by displaying both the current temperature and the relative humidity. The interplay between the temperature and the relative moisture content of the air strongly affects one’s sense of wellbeing, not only aboard ship, but also at home in one’s own four walls. The right combination of the two factors determines the so-called “feel-good climate.” As a rule of thumb: the higher the relative humidity, the lower the temperature needs to be for a person to feel comfortable. For example, people feel just as comfortable at 22.5° Celsius and 30% humidity as they do at 21° Celsius and 60% humidity. Wempe’s selection of comfort-meters includes a wide variety of these maritime “feel-good measuring devices.”

Ship’s bell clocks


Ship’s bell clocks were originally used as half-hour sandglasses. With the particular sequence of chimes tolled by a ship’s bell, they set the rhythm for the changing of the watches aboard ship. One bell indicates one half-hour of elapsed time. The seamen standing watch were relieved of their duty at four-hour intervals, i.e. every eight bells. As long ago as his voyages of discovery in 1492, Columbus relied on sandglasses to aid him in navigation and to help time the changes of the ship’s watches. Today too, the distinctive chime of maritime time measurement recalls an era when life on deck was not yet determined by high technology. As was the case centuries ago, the four-hour rhythm of the changing of the ship’s watches continues unchanged today.



For more than 200 years, hygrometers have served as reliable instruments to measure relative humidity and thus to predict the weather. Mariners have long known that the likelihood of fog formation is directly correlated with the relative moistness of the air. But few people are aware that the first device to measure atmospheric moisture was invented in the 14th century to serve an entirely different purpose: namely, to settle the age-old quarrel between buyers and sellers of wool. Their bone of contention: the same amount of wool weighed more on humid days than on dry days, and was accordingly more costly when the air was moist. Cardinal de Cusa (1401 -1464) deserves credit for inventing a device that could measure the relative humidity and thus enable wool merchants to standardise the net price at wool markets.



A thermometer can accurately measure temperature. The first such device was invented in 1610, and learned men have argued about a unified scale for thermometers ever since. Not until 1742 did the Swedish astronomer Anders Celsius succeed in constructing a mercury thermometer which, under a particular pressure, could subdivide into 100 parts the span of temperatures from the freezing point to the boiling point of water. Interestingly, the original boiling point was defined as 0 degrees and the freezing point as 100 degrees. This definition for temperature measurement was invented later. The Celsius scale is now widely disseminated throughout the world.

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