LECTURE XV.

THE PLANETS URANUS AND NEPTUNE .

“ When the planets,

In evil mixture to disorder wander,

What, plagues, and what portents ! what mutiny !

What raging of the sea ! shaking of earth !

Commotion in the winds ! frights, changes, horrors ! ”

Troihis and Cressida.

We must now take another gigantic stride, more than twiceas great as that which carried us from the orbit of Jupiter tothat of Saturn ; for our next step onwards, over the space thatintervenes between those of Saturn and Uranus , measuresalmost exactly 900,000,000 miles. It brings us to a planetwhose distance from the Earth is therefore always so enormous,that it is with difficulty that we can discover auy points ofinterest connected with it. Nor are we surprised that untilMarch 13th in the year 1781 its existence was altogether un-known ; or that, even then, when Sir W. Herschel unexpectedlydetected it, he thought that what he saw was a distant cometmoving amongst the stars visible in the field of view of histelescope.

And here we may draw special attention to one very interest-ing and instructive fact involved in the history of the discoveryof the planet Urauus, viz., that a certain peculiarity in itsappearance indicated to the experienced eye of that greatastronomer, within (as he himself has stated) a minute of hisfirst seeing it, that it was no ordinary star. There was ahaziness, and a comparative faintness about its light, whichhe at once noticed. This led him to apply a higher magni-fying power to his instrument, in order to see what etfectwould be thereby produced. Sir W. Herschel was well aware