χ _Persei._ Perceptible to the eye as a patch of hazy material lying between the constellations Cassiopeia and Persei. In a telescope it forms a double cluster, and is one of the richest and most beautiful objects that the sky affords. The tyro who first beholds it is astonished at the marvellous profusion of stars. It can be fairly well seen in a good field-glass, but its chief beauties only come out in a telescope, and the larger the aperture the more striking will they appear. It is on groups of this character that the advantage of large instruments is fully realized. The power should be very low, so that the whole of the two clusters may be seen in the field. An eyepiece of 40, field 65′, on my 10-inch reflector, presents this object in its most imposing form. κ _Crucis_. Sir J. Herschel’s observations at the Cape have made this object familiar to northern observers. It is composed of more than 100 stars, from the 7th mag. downwards; and some of the brighter ones are highly coloured, so that the general effect is greatly enhanced and fully justifies Herschel’s statement that the group may be likened to “a superb piece of fancy jewelry.” ζ _Ursæ Majoris_ (_Mizar_). This group is interesting both as a naked-eye and as a telescopic object. There is a 5th mag. star, named Alcor, about 11½′ distant from Mizar, and the former was considered a good test-object for unaided vision by the Arabian astronomers. But the star has probably brightened; for it can now be easily seen, and certainly offers no criterion of good vision. Mizar is a fine telescopic double, the companion being 4th mag. and distant 14½″. Any small telescope will show it, and there is another 8th mag. star very near. σ _Orionis_. This appears as a double-quadruple star, with several others in the same field. A 3-inch will reveal most of them, though some of the fainter stars in the group will be beyond its reach. θ _Orionis_. In the midst of the great nebula of Orion there is a tolerably conspicuous quadruple star, the components of which form a trapezium. This is visible in a 2-inch refractor. In 1826 Struve discovered a fifth star, and in 1830 Sir J. Herschel found a sixth; these were both situated a little outside the trapezium. All these stars have been seen in a 3-inch telescope. The great 36-inch equatoreal at Mount Hamilton has added several others; one was detected by Alvan G. Clark (the maker of the object-glass) and another by Barnard. These were excessively minute, and placed within the trapezium. Barnard[54] has also glimpsed an extremely minute double star exterior to the trapezium, and forming a triangle with the stars A and C on the following diagram:— [Illustration: Fig. 63. The Trapezium in Orion, as seen with the 36-inch refractor.]