Everyone talks about the weather. This is doubly true for sailors, where bad weather could mean a very bad day. So it isn’t surprising that navies around the world have had a keen interest in weather forecasting. But how did you predict the weather before modern instruments, radar, and satellite images? Vice Admiral Robert FitzRoy had great faith in “storm glasses,” a glass chamber containing some chemicals that he didn’t invent, but did document and promote heavily during the 1860s.

Did it work? Apparently not, but the device is still interesting in its own right. FitzRoy was a pioneer of meteorology, replacing folklore with actual observations and attempts at scientific rigor. While he did arm observation stations with conventional things like thermometers and barometers, he was also a proponent of the weather glass.

What is it?

The glass itself was a sealed glass vessel, often a tube, that contained a mixture of alcohol and water. In that mixture were camphor, saltpeter, and sal ammoniac.

The camphor will precipitate out or dissolve into the solvent, forming amazing crystal patterns. According to FitzRoy, the liquid will be clear if the weather is clear, and cloudy if it is cloudy outside. Different sizes of particulates indicate rain, snow, and other weather phenomena. FitzRoy thought the wind had “electrical tension” and that was responsible for the device’s ability to predict weather.

Scientific studies showed little correlation between the state of the glass and the weather. However, it is still a great conversation piece.

Despite the salts in the recipe, the spectacular crystals in a storm glass are primarily camphor. Camphor dissolves readily in alcohol but poorly in water, while potassium nitrate (saltpeter) and ammonium chloride (sal ammoniac) have roughly the opposite preference. The mixed alcohol-water solvent accommodates all three, but the camphor sits close enough to its solubility limit that temperature changes cause it to crystallize and redissolve. The salts appear to affect the form of the growing crystals, helping produce the elaborate dendritic structures that make the glass look so dramatic.

Maybe it Works?

FitzRoy was convinced the glass was effective. However, in 1863, Charles Tomlinson wrote in The Philosophical Magazine that the instrument was little more than a crude thermometer. This was later suggested in a 2008 article, as well.

Proponents of the glass will tell you that they need to be placed very carefully, out of climate-controlled areas. They also, apparently, say you have to initially heat the liquid until the crystals are totally dissolved. After a few weeks to adapt, they swear the Storm Glass is a perfectly good weather prediction system.

Despite their unreliable nature, the storm glass was a popular item, and you can even find them today, more as decor. But in 1863, you could find a variety of choices with and without thermometers attached, as you can see in the James J. Hicks catalog page.

Before the Glass

Of course, people were interested in the weather well before the late 19th century. Even FitzRoy admitted that the storm glass was at least 100 years old by his day. The game changer was the electric telegraph.

The telegraph allowed for widespread real-time observations. FitzRoy was a pioneer in that game, as was his mentor Sir Francis Beaufort, famous for developing the Wind Force Scale, sometimes known as the Beaufort scale. If you read his writings, he was, for the most part, on the right track for weather observations. But the storm glass that is most closely associated with his name wasn’t really the thing you wanted to be remembered for.

You can make your own storm glass, as you can see in [NightHawkInLight’s] video below. Maybe you can determine whether it really works. Or take your weather station into the modern era.

Featured image: Baromètre de Fitroy ou ou verre-de-tempêtes by [Anja]