In 1862  Rudolph Koenig (1832-1901) developed the manometric flame apparatus, which was used into the first decade of the twentieth century to examine the wave-shapes of sounds. The heart of the apparatus is the manometric flame capsule. In the Kenyon apparatus, sound enters the capsule from the left-hand side (probably conveyed there via a funnel and a length of rubber hose), and impinges on a rubber membrane placed between the two halves of the capsule. Illuminating gas enters at the bottom of the shaft and burns in a small flame at the upper right-hand corner. The oscillations of the membrane modulate the gas supply, and the height of the gas flame varies accordingly. The oscillating gas flame is viewed in the rotating mirror, which supplies the necessary time base to make the waveshape visible.

   The manometric flame in the Kenyon apparatus was made by Central Scientific, and the rotating mirror by Knott of Boston. The latter was sophisticated (and cost $9.75 in 1916); inside the mirror is a mechanical governor to keep the rotation rate constant. The capsule from St. Patrick's College (Maynooth, County Kildare, Ireland) is by Yeates of Dublin, and has two mouthpieces attached to it, one being used as a base. In use, one of the mouthpieces would be attached to the sound input tube on the left-hand side.

REFERENCE: Thomas B. Greenslade, Jr., "The Rotating Mirror", Phys. Teach., 19, 253-254 (1981)
                               Kenyon College                                                                             Grinnell College
                                    St. Mary's College                                                    St. Patrick's College, Maynooth, Ireland

This unmarked apparatus at Duke University combines the capsule and the rotating mirror on one base. It is probably German and from the first years of the 20th century.

At the left is a large manometric flame apparatus made by the firm of W. A. Olmsted of Chicago sometime prior to 1898, when the company was destroyed by a fire in which Olmsted was killed. It is 13 inches in height and the spun brass cone is removable.     At the right is an equally large rotating mirrors dating from about 1900. It is unmarked, but looks like a piece of apparatus by Max Kohl of Chemnitz, Germany.    This apparatus is in the Greenslade collection.

The maker's mark at the top of the manometric flame apparatus at the left is difficult to decipher, but it starts with "M" and ends with "O&Co.", suggesting that it was made by the McIntosh Battery and Optical Company of Chicago. This company sold out to Olmsted in May, 1897, setting an upper bound to the age of the apparatus.     REF: Thomas B. Greenslade, Jr., “Apparatus Manufacturers in Chicago, ca. 1900”, Rittenhouse, 13, 16-19 (1999)  The rotating mirror apparatus at the right is by Knott.    Both pieces of apparatus are in the Greenslade collection.

The unmarked manometric flame at the left is in the Greenslade Collection.

The manometric flame apparatus at the right is by Kipp of Delft in the Netherlands. I was not able to take it apart, but I think that the shielded leads are attached to a small speaker, which is directed downward to the vibrating membrane of the manometeric flame at the bottom. At the left is the gas supply, and the flame is at the right.     As such, this is a hybrid between the fully mechanical system of observing acoustical wave shapes with a manometric flame and a rotating mirror, and the fully electrical system using a microphone and an oscilloscope.     The apparatus is in the Greenslade Collection.