Piano construction in Europe and the USA from about 1820 to the 1860s was a period of intense experimentation and development. The strength of the case was an important consideration given the increases in string tension during this period. This lead to structural changes such as the addition of wooden and metal braces. Keeping the piano in tune was also integral to this development. The compensating frame used by Stodart is extremely significant in the development of the piano. It shows that a practical method to maintain a constant string tension and hence stability of tuning was being developed 30 to 40 years before the full cast-iron frame was used in Europe. The latter became a standard feature of grand pianos from then to the present day.
The innovation consists of a series of metal rods which expand or contract to changes in temperature thus allowing the strings of the piano to also expand or contract at the same rate. The rods are made of two different metals, brass for the bass strings and iron or steel for the mid range and treble. It appears that the inventors of this particular system were employees of Stodart, James Thom and William Allen who were granted a patent for "Improvements in pianofortes" No 4431 on January 15 1820.
Although the rationale behind the system was essentially in terms of allowing for climatic fluctuations it also benefited greatly in strengthening the piano against the massive tension put on it by the strings. This was to become a major focus of piano makers until the invention of the full cast-iron frame with cross stringing introduced into Europe by Steinway in 1862.
This particular instrument is described in two publications (see below) by Martha Novak Clinkscale and Stewart Symons.
Martha Novak Clinkscale; Makers of the Piano 1820-1860 (OUP, Oxford & New York, 1999 , p.361.)
Rosamond EM Harding; The Piano-Forte: its history traced to the Great Exhibition of 1851, (2nd Ed. Gresham Books, England, 1978 pp.202-208).
Stewart Symons, The Pianoforte Past, exhibition catalogue, Bradshaw Collection, Queen Street Galleries, Sydney, no date, p.14, item 17).
Thom and Allen Patent described in Patents For Inventions. Abridgements of Specifications Relating To Music and Musical Instruments, AD 1694-1866, 2nd Edition, London, 1871, (Facsimile edition, Tony Bingham, London, 1984, p.86).
Curator, music & musical instruments