1880.] NEW YORK ACA.DEMY OF SCIENCES. 253 



and the same observers have detected faint belts upon tlie disc, 

 which have also been seen at Nice, and by the Henrys in Paris. 

 Many of the observations appear to indicate a very paradoxical 

 fact — that the belts, and consequently tlie planet's equator, are 

 inclined to the orbits of the satellites at a considerable angle. 

 The mathematical investigations of Tisserand appear to demon- 

 strate that, in the case of a planet perceptibly flattened at the 

 poles, satellites near enough to be free from much solar disturb- 

 ance must revolve nearly in the plane of the equator; while 

 those more remote, and disturbed more by the sun than by the 

 protuberant equator of the planet, must revolve nearly in the 

 ])lane of the planet's orbit. Thus the two satellites of Mars, the 

 four satellites of Jupiter, and the seven inner satellites of Saturn, 

 all move nearly in the e([uatorial plane, while our moon and 

 Japetus move in ecliptical orbits. It is very difficult to believe 

 that the satellites of Uranus, which are certainly not ecliptical 

 and are very near the planet, do not move equatorially. And yet 

 it is unquestionable that most of the observations with suffi- 

 ciently powerful telescopes (my own among them) do seem to 

 indicate pretty decidedly that the planet's equator is inclined as 

 much as 15° or 20° to the orbit plane of the satellites. 



As to Neptune, there is nothing new. One or two old observa- 

 tions of the planet have turned up in the revision of old star 

 catalogues, and Hall, of Washington, has made a careful and 

 accurate determination of the orbit of its one satellite, and of the 

 planet's mass ; while Maxwell Hall, of Jamaica, has deduced a 

 very doubtful value of the planet's rotation from certain photo- 

 metric observations of its brightness. 



There has been some hope that a planet beyond Neptune might 

 be found. Guided by certain slight indications of systematic 

 disturbances in the motion of Neptune, Todd made an extended 

 search for it in 1877-8, using the Washington telescope, and 

 hoping to detect it by its disc, but without results. If such a 

 planet exists, it is likely to appear as a star between the 11th 

 or 13th magnitude, and may be picked up any time by the 

 asteroid-hunters. But its slow motion and the fact that our 

 present charts give but few stars below the 11|- magnitude, will 

 render the recognition difficult. 



The indications I have sjioken of, and certain others first 

 noted in 1880 by Prof. G. Forbes, and depending upon the be- 

 havior of certain periodic comets, fnrnish pretty strong reasons 

 for believing in its existence, though as yet they fall far short of 

 making it certain. 



Comets. 



During the past ten years we have been favored with an extra- 



