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Friday, July 19, 2013

A Change in the Weather?

It's about time for my annual heat wave post (check out last year's post for some great Cruikshank illustrations on how to beat the heat).  According to the weather forecasts, we are finally due for some heat-clearing storms, so I thought I'd highlight an item which could be used in understanding and predicting the weather. It is a wheel barometer. (I  apologize for the poor image: it is in storage and I couldn't get far enough away to shoot it square-on).


C.A. Canti, barometer. English, 19th century. 1954.2021   
The  reason it's known as a wheel barometer is pretty straightforward--the atmospheric pressure (and resulting weather) is read from a large dial (ours is over a foot across), as opposed to a "stick barometer" which has vertical markings like a thermometer.

C.A. Canti, barometer. English, 19th century. 1954.2021 
This type of barometer was invented in the 17th century by Robert Hook and involves a u-shaped tube filled with mercury; a float on the mercury is linked to the needle. You can see Hook's original diagram and read more about how the barometer works and about Hook's interest in weather at the Hook's London blog.  Ours is a 19th-century example; the nameplate indicates that it was made by C.A. Canti of Town Malling, Kent, who was in business ca. 1815-1845.

C.A. Canti, barometer. English, 19th century. 1954.2021 

This kind of barometer is often called a banjo barometer, due to its shape. The long neck holds the necessary tube, and also provides an excellent place to add other useful weather devices--such as a thermometer.

C.A. Canti, barometer. English, 19th century. 1954.2021 
It may be hard to see in this picture, but the thermometer is marked at several important points, such as freezing and "blood heat." I also noticed that "Sumr heat" is clearly marked--right at 76 degrees! Of course this was made in England, which is cooler than here, but they are having their own heat wave now and would probably be quite glad for that level of "summer heat".

C.A. Canti, barometer. English, 19th century. 1954.2021 
Stay cool and remember that  a visit to the Rosenbach is wonderfully air-conditioned.



Kathy Haas is the Associate Curator at the Rosenbach Museum & Library.

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