Properly a soft celeste made from one or two open or stopped flute ranks, the name Unda Maris has been used for both sharp and flat celestes made from a variety of stops, both flutes and strings. According to Wedgwood and Audsley, some French builders (e.g. Puget) used the Quintaton (see also Quintaphon). Norman & Beard used two Zauberflöte ranks, one tuned sharp and one tuned flat, in their organs in Norwich Cathedral, England (1889), and Christ Church, Lancaster Gate, England. Skinner's Unda Maris used Dulciana ranks, which Skinner considered to be a string, and was tuned sharp like all of his celestes. Skinner considered it to be native to the United States, but Grove and Williams date it from the 18th century in south Germany. Adlung describes this stop as a Principal rank tuned sharp and intended for use only with the normally tuned Principal. Maclean describes Gottfried Silbermann's Unda Maris as being of Diapason scale, and intended to be used with the 8' Principal (see Voce Umana). Adlung also states �at Waltershausen the Unda maris 8' is a rank with double lips that produces two sounds, one of which is somewhat sharper than the other.� Could this have been an early form of Ludwigtone? During the 20th century, this stop was commonly tuned flat, leading to a widespread belief that the name Unda Maris properly denoted a flat-tuned celeste, in spite of historical evidence to the contrary. The name Unda Maris means �wave of the sea�.
Osiris contains about 20 dozen examples of Unda Maris, all at 8' pitch except for nine at 4'. The earliest known examples are listed below. Only one example of the name Onda Maris is known, and no examples of Meerflöte. Contributions welcome.