SCIENTIFIC SUMMARY 
ASTRONOMY. 
Mars . — At the November meeting of the Royal Astronomical Society, 
Professor J. C. Adams read an interesting paper on the motion of the nodes of 
the satellites of Mars, and the important information which the observations 
of this motion would throw on the figure and constitution of the planet. 
Assuming that the planet was a symmetrical spherical body, Mr. Marth had 
shown, in the Astronomischen Naclirichten, No. 2280, that the nodes of the 
orbits of the satellites would have an annual motion, due to the Sun’s action, 
amounting to 0 o, 06 in the case of JPhobos, the inner satellite, and to 0 o, 24 
in the case of Deimos, the outer satellite. If, then, the satellites of Mars pre- 
served a constant inclination to the orbit of Mars, as would be the case were 
the planet a symmetrical spherical body, from the difference in the rate of 
motion of their nodes, they would in course of time have their orbits very 
much inclined to one another. So much so, that though at present the two 
satellites move in nearly the same plane, the plane coinciding with the plane 
of the equator of Mars, yet a thousand years hence they would move in 
orbits whose planes were inclined to each other by an angle of nearly 49°. 
Professor Adams draws attention to the fact that, if the planet Mars be not 
spherical but spheroidal, like our Earth, the effect of this deviation from a 
sphere would be to tend to make the satellites move in orbits very nearly 
coincident with the plane of the equator of Mars, and in this case the planes 
of the orbits of the satellite would always be nearly coincident, as they are 
known to be at present. As Laplace has shown, if the motion of the node 
due to the effect of the ellipticity of the planet be much greater than that 
due to the action of the Sun, the orbit of the satellites will always nearly 
coincide with the plane of the equator of the planet. Professor Adams now 
shows that, even if the planet be supposed to be only very slightly spheroidal, 
the effect of the ellipticity will very much exceed that of the Sun, so that the 
satellites will always move in orbits but slightly inclined to the plane of the 
equator of the planet. Now the effect of the ellipticity of the planet cannot 
be well determined from the motion of the node, because, owing to the 
slight inclination of the orbits, it will be difficult to accurately determine 
the motion of the nodes from observation. But the orbits of both satel- 
lites seem to be sensibly eccentric, and it will not be difficult to determine from 
