anew the ground gone over by Lexell, and was able to confirm substantially Lexell's conclusions. This remark, however, more especially applies to what Lexell suggested as to the influence of Jupiter, but Burckhardt varied Lexell's conclusions by suggesting that after the comet escaped from the clutches of Jupiter in 1779, its orbit was enlarged to an ellipse with a period of more than 16 years, and with a perihelion distance so great that the comet would for ever be at so great a distance from the Earth that we could never hope to see it again.
After the lapse of nearly half a century the orbit of Lexell's Comet was again investigated, and this time by Le Verrier, in a paper presented to the Academy of Sciences at Paris, in May, 1848. Le Verrier's calculations in some respects support, and in others differ from those of his predecessors, but the questions involved would occupy more space than it is convenient to allot to them in these pages. Hind's summary of them is as follows:—"The final conclusion from Le Verrier's investigations is that the Comet of 1770 may be considered lost until it is accidentally rediscovered in the ordinary course of searching for these bodies, when his formulæ will enable the astronomer to recognise in the new comet that interesting wanderer."
These words were written in 1852, and persistent have been the efforts of astronomers to find in each new short- period comet the old Lexell, but the results thus far have been inconclusive. It remains to be added that Brünnow has confirmed in part Burckhardt's calculations.
When Lexell's Comet on July 1, 1770, was at its minimum distance of about 112 millions of miles from the Earth, the visible diameter of the comet was, as already stated, 2° 23'; it follows therefore that the true diameter was 60,000 miles.
Biela's Comet.
On March 8, 1772, Montaigne at Limoges discovered a comet which, from the want of suitable instruments, he was unable properly to observe, or to observe at all after March 20.
