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Rh theory. All the same, it is desirable that the place where the star of 1572 appeared should be examined from time to time. Argelander has, from a discussion of all Tycho's distance-measures, found the most probable position of the star for the equinox of 1865 to be: RA = 0h. 17m. 20s., Decl. = +63° 23′.9. This position agrees remarkably well with that of a small star of the 10.11 magnitude, No. 129 of D'Arrest's list of stars in the neighbourhood of Tycho's Nova, which is for 1865: 0h. 17m. 19s. +63° 23′.1.

Whether this small star is variable or not must be left for the future to decide. Argelander stated in 1864 (speaking from memory) that he had about forty years previously failed to see any star in the place with the transit instrument at Åbo (of 5$1⁄2$ inches aperture), and that he had also later—probably in 1849—been unable to see anything with the transit circle at Bonn. There is thus a possibility that D'Arrest's star may have increased in light of late years, and observations made at Twickenham by Hind and W. E. Plummer in 1872–73, and at Prague by Safarik in 1888–89, seem to indicate that it is subject to very slight fluctuations of light. The map of all the stars in the neighbourhood, prepared by D'Arrest (which is complete down to the fifteenth or sixteenth magnitude, within a radius of 10′ from the place of the Nova) may in future be compared with photographs of this interesting spot, which deserves to be watched from time to time.