Symphony No. 3 (1995) was commissioned by the Würth Foundation for the Stuttgart Chamber Orchestra; première February 5, 1995, by the Stuttgart Chamber Orchestra, Künzelsau, Germany. Composed for the 19 string players of the Stuttgart Chamber Orchestra, Philip Glass's Symphony No. 3 was designed to treat every musician as a soloist. "The work fell naturally into a four-movement form," Mr. Glass has written, "and even given the nature of the ensemble and solo writing, [it] seems to have the structure of a true symphony."

The opening movement, a quiet, moderately paced piece, functions as prelude to movements two and three, which are the main body of the Symphony. The second movement mode of fast-moving compound meters explores the textures from unison to multiharmonic writing for the whole ensemble. It ends when it moves without transition to a new closing theme, mixing a melody and pizzicato writing. The third movement is in the form of a chaconne, a repeated harmony sequence. It begins with three celli and four violas, and with each repetition new voices are added until, in the final [variation], all 19 players have been woven into the music. The fourth movement, a short finale, returns to the closing theme of the second movement, which quickly re-integrates the compound meters from earlier in that movement. A new closing theme is introduced to bring the Symphony to its conclusion.

A string orchestra has its own sound that is both rhythmic and lyrical, a mixture of the bite of horsehair on strings, the plonk of pizzicato, and a singer's long cantabile phrases. In the Symphony's first movement, Philip Glass uses this attribute to show just how suspenseful C major can be. It has the character of a gripping movie score, thanks to its ventures into the dark, "flat" side of its harmony. In the second movement, slashing unison figures seem to recall the classic American symphony for strings, William Schuman's Symphony No. 5 of 1943. Mr. Glass also returns to his own earlier ideas in the third movement, with its deep string tone, syncopated rhythm, repeating chord progression, and vocal violin solo reminiscent of works such as the opera Akhnaten. The vigorous finale chugs to a 3+3+2 rhythm, punctuated by strange chromatic passages that yank the music into new harmonic territory.

the CIVIL warS (1984) was commissioned by Teatro dell'Opera di Roma; première March 1984, at Teatro dell'Opera, Rome, Italy. Glass composed the music for Act V, the final act of Robert Wilson's colossal stage piece the CIVIL warS: a tree is best measured when it is down, a day-long work intended for the Olympic Festival of the Arts at Los Angeles in 1984. Abraham Lincoln, Mary Todd Lincoln, Robert E. Lee, and personages from Native American and Greek mythology were among the figures who traversed the stage, singing in several languages and creating multiple visual tableaux.

"Wilson needed time for a scene change in a couple of places, and asked me for some music," Mr. Glass recalls. "I composed a sort of pause, a respite from the stage action. They were quiet pieces." One hears the distant sounds of Wagnerian horns or the exotic suggestions of the "Arabian Dance" from Tchaikovsky's Nutcracker. The influence of the latter work, and especially the descending-scale theme of its grand pas de deux, stands out in the second interlude.

The Voyage (1992) was commissioned by Metropolitan Opera in commemoration of the 500th anniversary of the discovery of America; première October 12, 1992, at the Metropolitan Opera House, New York. Between the two CIVIL warS interludes, we hear the "Mechanical Ballet" from Mr. Glass's opera The Voyage, composed in 1992 to commemorate Columbus's journey to America. The stage action brings together events widely separated in time, including not just Columbus's voyage, but a future space mission and a visit to earth by an alien spacecraft in prehistoric times as well. Alter the latter's arrival, an instrumental interlude was called for, which (according to Mr. Glass) the opera's director David Pountney dubbed the "Mechanical Ballet". As far as Mr. Glass knows, no reference to Ballet mécanique, the notorious 1925 piece by the American modernist George Antheil, was intended. For his part, the composer cites Verdi's Requiem and his own Einstein on the Beach as the main influences on this music.

The Light (1987) was commissioned by Michelson-Morley Centennial celebration; première October 29, 1987, by the Cleveland Symphony Orchestra, Cleveland, Ohio. "In school, I thought I'd want to be a scientist," Mr. Glass recalls. This is reflected in a number of his compositions: he has written about Einstein, based a character in The Voyage on the cosmologist Stephen Hawking, and is even involved in a prospective opera about Galileo. "The suggestion," he has written, "to write music to commemorate the anniversary of the Michelson-Morley experiment at Case Western Reserve University in 1887 was one to which I could respond immediately."

In their simple yet revealing landmark experiment, the American physicists Albert A. Michelson and Edward W. Morley used mirrors to split, reflect, and recombine a single beam of light, producing a fringe-like "interference pattern." The fact that this pattern was always the same, regardless of the motion of the apparatus, demonstrated that the speed of light is always the same, regardless of the motion of the observer. This stunning result was not explained until the publication, two decades later, of Einstein's theory of relativity.

In The Light, Mr. Glass depicts the light itself, and the inspired minds of the two scientists, by means of his most scintillating orchestration, strong on piccolo, trumpet, and violin arpeggios. Discovered by Americans, these light waves and particles seem to be dancing a foxtrot. Mr. Glass comments:

In a way, these experiments formed in my mind an almost 'before and after' sequence. The 'before' represented something like 19th century physics. The 'after' marks the onset of modern scientific research. Perhaps this may appear somewhat simplified from a scientific point of view, but for a musician it provided a dramatic contrast.

The music begins with a slow, romantic introduction and leads abruptly to the main body of the work — a rapid, energetic movement, which forms the balance of the music. The opening bars are heard again just before the final moments and the music ends quietly.

I have described this one-movement work as a portrait. In the past I have written portrait operas — Einstein, Gandhi, Akhnaten are the subjects of the first trilogy. In this case, this is a portrait not only of the two men for whom the experiments are named but also that historical moment heralding the beginning of the modern scientific period.

The video was conceived by Rich Bevan and examines associative relationships between sound, form and space, constructed according to a range of specific sonic and spatial scale rule sets (micro, component, meso and macro) which I designed as part of a cross-disciplinary notation/cartographic system.