103 
lem, together with new elements for each nucleus, and an 
ephemeris for each at the approaching return of the comet 
to perihelion. This I have not counted as one of the Me- 
moirs. His third and last paper on the subject appeared in 
May, 1860, under the title, “On Biela’s Comet.” It con- 
sists first of an admirable history of all our knowledge of 
this comet, with full references to the original sources, and 
presents an excellent specimen of what might be called con- 
densed detail. Next it contains an elaborate discussion of 
the observations and orbit for every recorded appearance. 
And in the discussion of the last appearance in 1852, he 
brought to light a new illustration of the mysterious alterna- 
tion of brilliancy between the two nuclei. For he showed, 
that when, on the 15th of September, Seccnr found both 
nuclei, and determined the position of one of them, the new 
one being too faint for observation, this so-called “new 
one” was the identical nucleus which he had discovered 
in August, and had been observing ever since; while the 
brighter of the two had then just become visible. “On the 
16th, the southern nucleus alone was visible; on the 17th 
and 18th, only the northern; and finally, on the 19th, both 
Were observed by Scout. The double observation was 
repeated at Rome and at Pulkowa, on the 20th, 23d, and 
25th ; while on the 21st only the southern, and on the 22d 
only the northern, was visible. We thus have a most in- 
teresting repetition of the, alternations in 1845-6, which 
now appear more remarkable only in consequence of the 
extreme faintness of the comets, which was such, that the 
slightest change of light sufficed to carry them within or 
beyond the scope of vision.” (Astron. Journal, VI. 140.) 
Finally, a recapitulation of the final elements for each 
nucleus, and for all the observations and normal places, ex- 
usts the sum of our present knowledge of Biela’s comet, 
