Page:A Dictionary of Music and Musicians vol 1.djvu/227
old accounts inform us—and were consequently subject to frequent injury from strain and friction; hence the constant appearance in old parish accounts of such entries as 'Paid for mending of the gret organ bellowis, and the small organ bellowis, vd.' These ever-recurring failures at length suggested the use of some more durable material, and wooden ribs were substituted for the leather folds. This improvement was effected as long ago as 1419, in which year, as we learn from the Fabric Rolls of York Minster, John Couper, a carpenter, received 'For constructing the ribs of the bellows, xiid.'
These bellows, however formed, could of course give only an intermittent supply of wind, being wholly inoperative while being drawn open; consequently two at the least were always required, one to supply wind while the other was replenishing. A more 'continuous' supply, though by no means of an 'unvarying' strength, was secured by the use of a contrivance like the ordinary smith's forge bellows, consisting of a feeder below and a diagonal reservoir above. When this form of bellows was first used, or finally abandoned, are matters not quite clear; but some disused specimens were lying in a lumber-room attached to Tong church, Shropshire, as late as the year 1789. Father Smith (died 1708) occasionally put something of the kind into his small cabinet organs; but attention was more particularly directed to the correction of the defects which continued to exist in the diagonal bellows.
A diagonal bellows was formed of two pairs of triangular-shaped ribs for the sides, a pair of parallel ribs for the spreading end, a bottom-board, a top-board—all attached together by leathern hinges—and the superincumbent weights. For a long time the bellows were placed with the bottom board in a horizontal position, the top board rising, and the whole taking the following outline when inflated:—
This did not however produce a uniform current of air, but a somewhat lighter one at the commencement of the descent, and a gradually increasing one during the closing. This arose from two causes. The first was connected with the weights. A weight exercises its greatest influence on a horizontal surface, and loses some of that influence on an inclined plane. The second was due to the varying position of the wooden ribs. These would present an obtuse angle to the wind in the bellows when inflated, thus—
and one gradually increasing in acuteness as it closed—
The top weights acquiring greater influence as the top board approached a horizontal position, and the side and end folds wedging their way into the wind, the two actions gradually increased the density of the wind to one-fourteenth beyond its first pressure. Various ingenious means were devised for correcting this inequality—as accumulative springs; a counterpoise acting in opposition to the descent of the bellows; a string of leaden weights which were left in suspension as the bellows descended, etc.: but the simplest and perhaps most effectual of all was that adopted by some of the German organ-builders, which consisted in placing the bellows so that the top board took the horizontal position on the bellows being inflated—
In this case the top weights exercised their greatest pressure at the starting, at which time the ribs exercised their least, and vice versa.
A bellows nevertheless still gave but an intermittent supply, and it was not until the year 1762 that an approach towards a successful combination of a feeder and a reservoir was made, by a clockmaker of the name of Cumming. This bellows had something of the form shown in the following outline:—
It presented the mistake however of having the two double sets of ribs folding the same way, which continued the defect in the increasing pressure of wind during the closing, that has already been noticed in the diagonal bellows. This led to the upper set being inverted, thus—
The upper set thus giving more room to the wind as the lower gave less, the one remedied the defect the other was calculated to cause. Thus the desired 'copious, unvarying, and continuous' supply of wind was at length secured.
There are certain disturbances which arise from the manner of the consumption of the wind.
It is essential that the bellows of an organ should yield a steady as well as an ample supply. The improved bellows being capable of the latter, the even flow was nevertheless apt to be disturbed from one of many causes. A prolific source of unsteadiness was unskilfulness on the part of the blower. At the commencement of the stroke the wind, in passing into the reservoir, has to overcome the pressure of the surface weights and taise the top-board, and at its