stars from the first to the seventh magnitude, inclusive, falling within 4" of each other if the stars were fortuitously scattered over the whole heavens to begin with. And, further, he has shown that the chances are 170,000 to one against any such stars, if fortuitously scattered, falling within 32" of a third so as to form a triple star. The chances against any such grouping as that seen in the trapezium of Orion are enormously greater than the numbers given above, and the inference is irresistible that these stars are in some way physically connected. We shall see, too, that it is also probable that these stars are in some unknown way related to the surrounding nebula.
Fig. 3.
Central and most brilliant portion of the Great Nebula in the Sword-handle of Orion, as observed by Sir John Herschel in his 20-foot Reflector at Feldhausen. Cape of Good Hope (1834 to 1837).
In 1811 Sir William Herschel was led to suspect changes in the form and brightness itself: an inference which he probably drew from a comparison of the early drawings with the appearance of the nebula as he saw it in his own reflectors; and in 1824 the younger Herschel made a drawing of the nebula and the stars immersed in it, as shown by his 20-foot reflector.
This drawing and a description of the nebula are given in "Memoirs of the Royal Astronomical Society," vol. ii., p. 489, and a copy of the drawing, so far as the small stars immediately about the trapezium are concerned, is given in Fig. 4.
The recession of the nebula from the stars of the trapezium is here
