Description

This thermograph is an instrument contained in a metal box with a rectangular glass window in the front. The box has a metal protuberance at one end, and a loop handle on the top. There is a latch on the front of the base of the instrument; releasing it allows the top of the case to lift open along the bottom edge. Inside the box there is a tall cylinder that reaches to the top of the instrument, and is covered in grid paper marked on the bottom with days of the week. The grid marks out temperature from 30° to 100°. A metal arm with a pen nib rests atop of the paper. The arm is connected on the other end to the mechanism mounted outside the case.

Thermographs are instruments that graphically give a continuous record of atmospheric temperature for a discrete period of time. In this thermograph, the cylinder measures a week of temperature at a time. This thermograph relies on a technology called the Bourdon tube. The French engineer Eugene Bourdon (1808-1884) developed a gauge that consisted of a tube filled with alcohol bent into a coil with a pointer attached to it. As the pressure in the tube changes, the coil winds or unwinds, moving the pointer. That pointer is attached to a pen nib, which traces a line on the cylinder and records the ambient temperature.

This instrument was manufactured by Julien P. Friez and Sons, a manufacturer of weather instruments founded in 1876 in Baltimore, Maryland. This instrument was manufactured for the U.S. Army Signal Corps.

Type

plaque

Location

inside, bottom

Text

Signal corps / U.S. Army // Thermograph ML-77 // Serial No. 417 Order no 3590-WF-43 // made by // Julien P. Friez & Sons // Baltimore Maryland