Fig. 84.—Details of the ring of Saturn observed by Trouvelot with the 26-inch Washington Refractor.
In close double stars therefore, or in the more minute markings of the sun, moon, or planets, we have tests of its defining power; and if this is equally good in the instruments examined, the revelations of telescopes as they increase in power are of the most amazing kind.
A 3¾-inch suffices to show Saturn with all the detail shown in Fig. [83], while Fig. [84] shows us the further minute structure of the rings which comes out when the planet is observed with an aperture of 26 inches.
In the matter of double stars, a telescope of 2 inches aperture, with powers varying from 60 to 100, should show the following stars double:—
| Polaris. | |
| α | Piscium. |
| μ | Draconis. |
| γ | Arietis. |
| ρ | Herculis. |
| ζ | Ursæ Majoris. |
| α | Geminorum. |
| γ | Leonis. |
| ξ | Cassiopeæ. |
A 4-inch aperture, powers 80-120, reveals the duplicity of—
| β | Orionis. |
| ε | Hydræ. |
| ε | Boötis. |
| ι | Leonis. |
| α | Lyræ. |
| ξ | Ursæ Majoris. |
| γ | Ceti. |
| δ | Geminorum. |
| σ | Cassiopeæ. |
| ε | Draconis. |
A 6-inch, powers 240-300—
| ε | Arietis. |
| 32 | Orionis. |
| λ | Ophiuchi. |
| 20 | Draconis. |
| κ | Geminorum. |
| ι | Equulei. |
| ξ | Herculis. |
| ξ | Boötis. |
An 8-inch—