The Hygrometer

The subject of my research and presentation is Leonardo’s hygrometer and its history. Over the course of the past few months when I’ve brought up this topic to my friends I am usually met with the same response. “What is that”? “Sounds like Ancient Greek to me”. Well, as a matter of fact, it is Ancient Greek! The etymological breakdown of the word hygrometer reveals two stems: hygr – meaning moisture, and meter – meaning to measure. From this knowledge, sans research, we are able to infer that a hygrometer is a device that measures moisture. This etymological knowledge of the Ancient Greek is actually what led me to this fascinating topic. I was attempting to choose a research topic and I was able to decipher what a hygrometer was, so I decided to investigate further. In my research, I happily discovered that I had guessed correctly about the function of a hygrometer.

Today you can find a modern, digital hygrometer, and even access the information on your phone. For our purposes I will be looking at the Hygrometer(s) of Leonardo Da Vinci and the Renaissance, which are much more rudimentary. As the article “Studies on Historical Gravimetric Hygrometers” by Erich Robens, succinctly puts it, “These instruments that measure the humidity of the air consisted of balances loaded with a hygroscopic material (125).” A hygroscopic material is any material that will absorb, or “see”-scop, the moisture from the air. Some examples of hygroscopic materials are wool, sponges, and even hair, as we will see later.

A familiar theme with Leonardo’s inventions that we have seen time and time again, is that he is usually not the first one to have come up with a hypothesis, concept, or prototype. The hygrometer is no different. Hygrometric practices are described in numerous historical sources, both of relatively recent periods, as well as ancient times. Some consider a passage from the bible to be an example of an early experiment of volumetrics, in the Talmud Book of Judges (“Early History” 426). Nicolaus Cusanus is regarded as the first “modern” inventor to propose a hygrometric device. His version featured a balance with wool on one end and stones on the other (“Early History” 428). The general principle is that as humidity in the air increased, the wool would absorb it and become heavier. The stones on the other hand, would remain at a static weight. The weightier wool would tip the balance, and one could visually see an increase in air humidity. The hygrometer could use any non-hygrometric material, not just stones. One source describes a balance-style hygrometer that uses wax (Svennberg 13).

Another renaissance figure, Leon Alberti suggested a similar device using sponges (“Studies on” 126). Leonardo later sketched in his notebooks proposed hygrometers using wool, sponges,and cotton (“Studies on” 126). He also had another sketch that included a balance with glass orbs on its ends, with one end also covered in fabric (“Early History” 429).

Erich Robens points out a very interesting fact about Leonardo’s hygrometer sketches: they were drawn on notebook pages that also included sketches for the Last Supper (“Early History” 429). He proposes that Leonardo may have been attempting to take atmospheric humidity into account when deciding what type of paint to use for his masterpiece. This theory only emphasizes the interdisciplinary practices that were characteristically unique to Da Vinci. Whereas Alberti and Cusanus may have been more interested in predicting storms, Leonardo wanted to apply that knowledge to the properties of paint.

Raymond Stites’s article, “Sources of Inspiration in the Science and Art of Leonardo Da Vinci”, dives into more fascinating specifications. Sketches of Leonardo’s proposed hygrometers can also be found among his sketches for the Adoration of the Magi, which we are able to date circa 1478 (234). Stites further elaborates that this hygrometer is very similar to one of Cusanus’s designs. While Leonardo is known for his practice of experimentation over relying on previous knowledge, many of his influential theories, designs, and machines were inspired by the works of others. It is possible that Leonardo’s hygrometer may also fit this pattern.

Cusanus’s, Alberti’s and Da Vinci’s propositions all came within a century of each other. Even after the Renaissance, the study of hygrometry did not stop, and in the 1700s, Horace- Benedict de Saussure created a hygrometer that used hair as its hygrometric material (“Early History” 429). I can certainly vouch for the fact that hair does increase in length and volume when exposed to environmental humidity. Other experimental hygrometers dealt with gravity and used various materials including paper. A public fascination with hygrometers continued long past Leonardo’s day and even became a “fad” in home decor for upper class citizens (“Early History” 430).

From my research, it is unclear whether Leonardo build a model of his hygrometer. Or perhaps it is unclear if he did, if it survived for us to know that he did indeed build it. Whether or not Leonardo translated his sketched designs into a tangible model, the hygrometer and its scientific and cultural significance did not end with him.

Today it might seem as if a hygrometer does not really matter. With modern meteorology technology and the internet, finding out if it is going to rain requires much less work than indirectly measuring the humidity of the air. To really value the significance of the development of a hygrometer, one has to think about the world in which its developers lived. They lacked many of the technologically advanced luxuries that are taken for granted today. In a world without our modern tools and weather.com, for man to be able to measure and predict nature using his own inventiveness and some wool seems downright revolutionary.

Sources:

Kiefer, Susanne and E. Robens. “Some Intriguing Items in the History of Volumetric and Gravimetric Adsorption Measurements.” Journal of Thermal Analysis and Calorimetry, vol. 94, 2008, pp. 613-618. Springer Link. https://link.springer.com/content/pdf/10.1007%2Fs10973-008-9351-1.pdf. Accessed 08 March 2018.

Middleton, W. E. Knowles. “The Early History of Hygrometry, and the Controversy Between De Saussure and De Luc.” Quarterly Journal of the Royal Meteorological Society, vol. 68, No. 297, October 1942, pp. 247-261. Wiley Online Library. http://onlinelibrary.wiley.com/store/10.1002/qj.49706829702/asset/49706829702_ftp.pdf?v=1&t=jed5hkiw&s=c7772a3acafb28c3bb2aeb7ca92655750432cabe. Accessed 08 March 2018.

Robens, Erich, and Shanath Amarasiri A. Jayaweera. “Early History of Adsorption Measurements.” Science & Technology, vol. 32. No. 6, 2014, pp. 425-442. Sage Journals. http://journals.sagepub.com/doi/pdf/10.1260/0263-6174.32.6.425. Accessed 08 March 2018.

Robens, E., et al. "Studies on Historical Gravimetric Hygrometers." Thermochimica Acta, vol. 235. 1994, pp. 125-133. Science Direct. https://ac.els-cdn.com/0040603194800901/1-s2.0-0040603194800901-main.pdf?_tid=d0116168-f51c-4344-bcf9-4cd063cde4f9&acdnat=1520189197_a4c5a6717362b9c3bb6887cd45f59ced. Accessed 08 March 2018

Stites, Raymond S. “Sources of Inspiration in the Science and Art of Leonardo Da Vinci.” American Scientist, vol. 56, no. 3, 1968, pp. 222-234. JSTOR, www.jstor.org/stable/27828187. Accessed 08 March 2018.

Svennberg, Kaisa. Determination of Moisture Properties for Materials Exposed to the Indoor Air. Licentiate Thesis, Lund Institute of Technology, 2003. http://www.lth.se/fileadmin/byfy/files/TVBH-3000pdf/KAS-3042.pdf. Accessed 08 March 2018