London: Royal Society. 1st Edition. Complete volume. FIRST EDITION OF THOMAS YOUNG’S LIGHT INTERFERENCE EXPERIMENT (the double-slit experiment) -- THE 1ST SERIOUS CHALLENGE TO THE PARTICLE THEORY OF LIGHT, THE 1ST STRONG EVIDENCE FOR & DEMONSTRATION OF THE WAVE THEORY OF LIGHT, & THE 1ST UNASSAILABLE EVIDENCE THAT “FRINGES ARE PRODUCED BY INTERFERENCE OF LIGHT WAVES” (DSB XIV, 566). Young’s persuasive experimental display, widely considered one of the most beautiful experiments in physics, was the first lucid proof that light added to light can produce alternate regions of darkness. ALSO INCLUDED: WM. HERSCHEL’S PAPER PROVIDING THE FIRST OBSERVATIONAL EVIDENCE THAT NEWTON’S LAWS OF GRAVITATION HOLD OUTSIDE OUR SOLAR SYSTEM.
Prior to the paper offered here, the British polymath Thomas Young delivered lectures at the Royal Society speculating on the idea of light as a wave & presenting a new concept, the principle of interference – the process in which two or more waves of the same frequency combine to cancel each other.
The principle upon which Young’s elegantly simple experiment rests is the division of a wave in space into two distinct parts which are then brought together to interfere. Young understood sound as a wave phenomenon -- meaning that if two equally intense waves of sound meet at a point, no sound would be heard because the waves would ‘interfere’ with each other; they would cancel each other out.
Young suspected that if light was also a wave phenomenon, then a similar ‘interference’ effect should occur. In his light interference experiment, he first “exposed a small piece of paper to sunlight diverging from a pinhole. The shadow exhibited not only fringes of color, but ‘…the shadow itself was divided by similar parallel fringes…’ Then, by inserting a small screen into either edge of the shadow, he was able to make the fringes disappear [to ‘interfere’ even though]… the light inflected on the other side was allowed to retain its course…[Hence] these fringes were the joint effects of the portions of light passing on each side of the slip of card, & inflected…into the shadow” (ibid). Another way to put it is that when light emerges from the two slits superimposed on the screen, a pattern –an ‘interference pattern’ -- of regularly spaced bright & dark fringes appears on the screen.
Wm. HERSCHEL’S DEMONSTRATION THAT THE ORBITAL MOTION OF THESE DOUBLE STARS OBEYS NEWTON’S LAWS OF GRAVITY & MOTION. Herschel wanted to show the physical relationship, the mutual gravitation, between double stars; he wanted to prove that they are “‘not merely double in appearance, but must be allowed to be real binary combinations of two stars intimately held together by the bond of mutual attraction’”( Macpherson, Herschel, 56). “The importance of [Herschel’s] discovery of binary stars” is fully realized “when we recollect that previously there was no scientific proof of the prevalence of the law of gravitation outside of the Solar System” (ibid).
Herschel’s observations of the orbital motions of CASTOR showed “a progressive alteration in the direction of the line joining its two components, of such a character as to leave no doubt that the two stars were revolving round one another…thus showing “that the double star was really formed by a connected pair of stars near enough to influence one another’s motion…It was an obvious inference that the motion of revolution observed in a binary star was due to the mutual gravitation of its members…This may be regarded as the first direct evidence of the extension of the law of gravitation to regions outside the solar system” (Berry, A Short History of Astronomy, 343). The proof itself would come in another five years when more observational precision was possible. Item #1212
CONDITION: 4to. 9 plates. Old faded stamp on rear of foxed title page, otherwise bright & clean within showing only light toning at the edges. Handsomely rebound in calf. Tight. Solid. 5 raised spine bands; gilt-lettered red & black morocco spine labels. New endpapers. Fine.