The Original Weather App: A 1915 Pocket Forecaster by Negretti & Zambra

February 03, 2015

In addition to books, Alembic also stocks a select group of beautiful and unusual scientific objects. One of my favourites at the moment is this charming, early 20th-century "Pocket Forecaster" by Negretti & Zambra.

The firm of Negretti & Zambra was founded in London in 1850 and quickly became a leader in the manufacture of precision scientific instruments, particularly barometers. Production of these pocket forecasters began in the early twentieth-century, probably around 1915 when the patent was granted. The forecasters are constructed of three celluloid dials, the outer two in an opaque cream with the inner dial being translucent so that the markings can be read. To predict the weather for the next twelve hours one simply adjusts the dials to the correct position for the direction of the wind and the current barometer reading (also noting whether the pressure is rising, falling, or holding steady), and compares the alphabetical results in the three windows at the centre to the legend printed on the back:

For instance, wind from the southwest and the barometer at 3.5 and falling gives a result of D and H, which translates to "Fine, becoming less settled" and "fairly fine, showery later". Though they were probably about as accurate as any weather prediction tool could be in 1915, these pocket forecasters seem to have been very popular. The National Maritime Museum at Cornwall holds a pocket forecaster which was donated by the son of a sailor on the English Channel. Our example is particularly nice in that it comes with the original box and instruction booklet.