While these names suggest a stop imitative of the modern orchestral or “French” horn, their meanings are often different. According to Williams, in the 16th century the names Horn and Hoorn frequently indicated a Cornet mixture, especially in the Netherlands and northern France. Audsley gives us the first known citation of an organ stop named French Horn, in a 1724 instrument by Renatus Harris at “St. Dionis Backchurch”. Audsley also reports that the orchestral horn was first used in England in 1720. Other sources, however, point out that Harris's horns stops, as well as those of his contemporary Bridge, were of trumpet quality, though slightly muffled.

Indeed, it was not until the mid-1700's that the technique of “stopping” a horn with the hand was developed, and with it the characteristic muffled and mournful tone of the French horn. Furthermore, this technique was developed as a means of obtaining notes between the harmonics on a natural (valveless) horn. Valves were not invented until around 1815. Thus, it was not until the 19th century that organ-builders began attempting to imitate the sound of the “stopped” orchestral horn, and these attempts did not achieve much success until the beginning of the twentieth century. Prior to the 19th century, horn tone meant “open” horn tone rather than “stopped” horn tone. This tone is represented in the organ by the Waldhorn.

A few noteworthy examples are worth examining in detail. Bonavia-Hunt, writing in the early 1920's, tells us:

Originally the attempt had been made by Mr. John Compton and others to develop the horn tone from oboe pipes fitted with excessively wide bells (about 6in. diameter at the top for the 1 ft. pipe). The great objection to the wide bell is the amount of soundboard space it occupies. The latest method is to voice an ordinary chorus reed (say 4 1/2 in. at CC, 8 ft.) on the close side on heavy pressure (from 12 in. upwards), employing double length (harmonic) pipes from tenor F up, with relatively thick tongues weighted fairly high up the scale, and “filled-in” shallots. The chief difficulty associated with close reed voicing is the tendency of the reed to “choke”, during which phenomenon the octave note below is heard along with the unison. By increasing the thickness of the tongue and fitting a baffle to the head of the shallot (a device introduced by Vincent Willis), this defect can be obviated.

Wedgwood provides a drawing of Compton's French Horn, the topmost illustration reproduced here. He gives the dimensions of treble C as 2' 3" long, and 6" across the bell. Audsley writes of two other examples:

The most successful Horn which has come under our notice is that recently produced by the Hook & Hastings Company, organ-builders, of Kendal Green, Mass. [USA], through whose courtesy we are able to describe and illustrate the formation of the pipes of the stop. It will be seen, on referring to [the middle illustration reproduced here], that the resonator is mainly of the inverted conical form, but differing from all other resonators of the form, in being closed at top with a conical cap, soldered on, and having a slot, with double adjustment for regulating and tuning, cut close to its upper end, as shown. It can be readily understood that the peculiar cap exerts a considerable mellowing effect on the tone in conjunction with the adjustable slot through which alone the subdued sound finds fre egress. The measurements of the pipe are as follows: The length of the resonator, exclusive of the conical cap, is 2 feet 3-3/4 inches; height of cap internally 5/8 inch. Length of slot (subject to alteration) 2-1/16 inches; width 9/16 inch; distance from top edge of resonator 1-1/2 inches. The measurements of the sound-producing portions are: The length of the reed (éschalote) from under side of the block is 1-3/4 inches, the width of the tongue at its free end is 11/32 inch, and where it enters the block 3/16 inch. The reed is of the closed form, its perforation commencing 5/16 inch from the lower end.

The second noteworthy example is the Horn which Mr. E. M. Skinner, organ-builder of Boston, Mass., added some years ago to the list of imitative stops. The formation and proportions of the pipes of this stop forcibly illustrate by what very dissimilar treatments similar results are obtained. In this case it may be stated that the resonator, instead of being of large scale and after the Trumpet model, is extremely slender and, accordingly, very slightly tapered. Also unlike that of the other Horn, it is open at top, and has a short cylindrical portion carrying an adjustable slide shaded by a partially attached disc of metal. The measurements of the tenor C pipe are as follows: The length of the resonator is 3 feet 3-1/2 inches (subject to slight alteration), and its internal diameter at top is 1.63 inches. The measurements of the sound-producing portions are: The length of the red from under side of the block is 2-3/16 inches; the width of the tongue at its free end is 7/16 inch, and where it enters the block 7/32 inch. The reed is of the closed form, its perforation being about 1-3/16 inches long, commencing about 3/8 inch from the lower end.

Audsley provides a drawing of Skinner's Horn, which is reproduced in the lowermost illustration given here. This was by no means Skinner's last word on the subject. Skinner himself writes:

The first example of the French Horn was made for an organ built for Grace Chapel, Williams College, Williamstown, Massachusetts.

The top of the pipe is capped, the tuning slot placed somewhat below the cap, thereby forming a pocket which varies in proportion to the diameter. The depth of the pocket was determined in the course of developing the character of the stop and is arbitrary, due to its substantial influence on the tone quality. The shallot of the French Horn is one octave larger than that of an 8' Trumpet. The opening, however, is of normal size and position, which places the over-length entirely below it forming a pocket in the lower end of the shallot. The combination of a pocket in the top of the pipe with a pocket in the shallot provides an acoustical range which permits sharp tuning without loss of stability. It is well known that the sharper a reed is tuned the smoother it becomes. So, in the French Horn, the pockets allow a smoothness in tuning, productive of that muted quality so characteristic of the orchestral Horn. However, since the “bubble” is present in both instances, a slight reconciliation is apparently necessary as in the case of the orchestral instrument, which contributes still further to its orchestral character. The cap and upper pocket are the features which provide the veiled quality to this voice.

When I heard it played for the first time, it exceeded expectations. It was and is the orchestral voice itself, even to the peculiarity in attack known as the “bubble”. In the first instance I made tenor C with an 8' shallot having a 4' C opening. This made the 4' C opening the precise size and distance from the block normal to a 4' C Tuba. In addition to the presence of the pocket, the shallot is one octave larger than is normal to the note. The top of the resonator is capped and the top of the tuning slot cut well below. This forms a pocket in the upper end of the pipe which, at low C, has a depth of six inches. The cap is of heavy metal to prevent vibration. Covering the top is equicalent to muting the orchestral horn by hand. The tongues require little weight.

The authenticity of this French Horn depends upon a precise depth of the pocket at the top of the pipe. Some builders have provided a tuning roll at the upper end of the tuning slot at the top of the resonator by which the depth of the pocket may be varied. This unwise expedient makes it easy for uninformed tuners to vary the pocket. ... The French Horn is of normal length throughout. It has relatively few weighted tongues which pecularity was most unexpected, as this of all reeds, is tuned the smoothest at the tuning wire.

The French Horn of the theatre organ seems not to have differed dramatically from that of the classical organ. It was, according to Strony, included only on larger instruments, the best examples being by Skinner and Kimball. Strony also comments that (unusually for the theatre organ) it is best used without tremulant.

Horn is also a synonym for Hörnli, and Corno is also a synonym for Cornetto.

See also Muted Horn.

Variants