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According to the commonly received ration of light in a Newtonian reflector and an automatic refractor, (which I believe to be very near the truth), the illuminating power of W. Lassell's 20-foot Newtonian of 24 inches in apertune is equal to that of a refractor of about 14 inches in aperture; which is more than three times the illuminating power of your large refractor. These large refractors will therefore prove extremely efficient on nebula, and on parish Satellite, and the Milky Way or: but on the minute phenomena of a planetary surface they fail in comparison with refractors of far inferior size, in consequence of the inequalities of figure inseparable, I fear, from the system of mechanical appropination employed in the process of figuring. Were it not for this source of imperfection, the large reflector of dead Rope, with its 6-foot diameter, might long ago have settled all questions respecting the small and close satellites of Uranus, the number of satellites attached to Neptune, the details of the phenomena on the surface of Saturn, so far. But, so far from this, it is a singular fact that we are not indebted to this enormous telescope for any planetary discoveries whatever! - not even in satellites!!
It is very gratifying to me to see that you are attending to the measurement of Double Stars. - I have observed but little this Spring, - my health having been far from good. In some instances, my measures of stars in your list (in No. of Astr. Nachr., in which are many very interesting things to which I have not now time to refer,) agree very closely with yours. Of γ Virginis I obtained, 1855 '33 P = 171 '18; D = 3 "'362; on 4 nights, with a double-usage microm by Amici. 1855 '46 P = 171 '17; D = 3 '308; on 5 nights, with with the parallel-wise micrometer.
Of ε Boötes I obtained the following
1854 '52 P = 322 '99; D = 2 " '686; and on 3 nights, with parallel wise microm. 1855 '53 P = 323 '63; D = 2 '638; - 1 night, with double image micr. by Amici.
Like yourself, I have been much interested with the appearance of Jupiter. The dark cap on the north pole is split up into immeasurable

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