The Leonid meteor shower was approaching and as the astronomers prepared cameras to capture the event they must have wondered: will the skies be clear tonight?
Prof. Winslow Upton taught astronomy at Brown from 1883 until his death in 1914. He also had a keen interest in meteorology. He had been a professor of meteorology at the Weather Bureau of the U.S. Signal Survice from 1881 until 1883. In 1884 he was one of the organizers of the New England Meteorological Society and operated a weather station at Ladd Observatory starting in 1890. We can gain some insight into how he might have forecast the cloudiness of the sky by noting a curious instrument to the left of the cameras in the photo above.
The Brashear spectroscope would usually have been attached to the main telescope to observe the absorption lines of stars. Here we see it mounted at an angle to observe the sky. The instrument has a very narrow field of view which would make it almost impossible to capture the spectra of a moving meteor. The small aperture and slow photographic plates wouldn’t have been sensitive enough to record the light. The most likely explanation is that it was used to observe the spectral lines of water vapor in the atmosphere to forecast rain.
There were a number of scientists during this era who attempted to use systematic spectroscopic observations to predict rain. They thought that a trained observer might be able to carry a “rain-band spectroscope” that was small enough to fit in a pocket. While there was some correlation between the darkness of the spectral lines and relative humidity it did not prove useful in predicting rain.