1868. | Astronomy. 71 
period 24h. 37m. 23°73s., in place of the period 24h. 37m. 
27°745s., first obtained. 
Mr. Cayley gives an expression for the angular distance of two 
planets, the sun being the centre of reference. Those who are inter- 
ested in questions of this sort, will be able to judge of the nature 
of the paper from the statement that,—v and v ' being the longi- 
tudes of the two planets in their orbits, $ and 4’ the longitudes of 
their nodes, and ¢ and ¢' their inclinations, then Mr. Cayley 
finds an expression for the required angular distance, in terms of 
cos (v—v'), sin (v—v'), cos (v+u'), and sin (vt v’), the coeffi- 
cients involving the quantities , 6', ¢, and 9’. 
Mr. Gill supplies a note on the Trapezium of Orion. He was 
able, with a good achromatic only 33 inches in aperture, to detect 
the exceedingly minute star 7 of the Trapezium. He also sus- 
pected the presence of a more minute star similar in R, A. to 9, and 
having the same declination as 3. It may be noticed in passing, 
that 6 of the Trapezium has been seen, with an achromatic only 3} 
inches in aperture, by Cooke. 
It appears that, after all, the variable T Coron, whose sudden 
appearance so startled the astronomical world in May, 1866, may 
have been visible before evening set in, in England, on May 12th. 
For Mr. Walter, surgeon of H.M.’s 4th Regiment, in North India, 
saw the star shining at least as brightly as Alphecca at eight o’clock 
on the evening of that day, an hour corresponding to about half- 
past two in the afternoon at Greenwich. It seems possible therefore 
that Mr. Stone was mistaken in rejecting the evidence given by Mr. 
Barker, of Canada ; evidence, however, which we are bound to say 
bore a very questionable appearance. 
Mr. Weston supplies a paper on the appearance of Jupiter’s 
satellites and their shadows when transiting Jupiter’s disc, on the 
evening of August 21st, 1867. He records the apparition of false 
satellites adjacent to the true ones, and distinct from the shadows. 
Such appearances, which have been observed by others, must, we 
think, be referred to optical delusion, since Mr. Dawes and other 
observers of the first class have failed to notice them. Mr. Weston, 
using a 9-inch Newtonian reflector, noticed that the shadow of the 
third satellite seemed larger than that of the fourth, an appearance 
which—as we have already said—seems to have been presented in 
almost every case, to observers who used reflecting telescopes. 
Mr. Leeson Prince, in a paper on the same phenomenon, calls 
attention to the fact that the remarkable darkness sometimes ob- 
served in the fourth satellite when transiting Jupiter’s disc, was 
observed and recorded nearly a century-and-a-half ago by Mr. J. 
Pound. This well-known astronomer took the satellite for its 
shadow, so dark was the former; and was surprised—soon after 
seeing the dark spot which he thus mistook—to see another and 
