Sidereal System called the Milky Way. 85 
one plane. The structure then of the Milky Way which we 
have been considering requires some modification. 
This modification is suggested by an observation of Sir J. 
Herschel, the son of the above-named, who, inheriting the ge- 
nius of his father and trained by an excellent scientific education, 
is now one of the luminaries of British science. ‘This astro- 
nomer, while residing at the Cape of Good Hope, wrote to 
a distinguished Italian mathematician, Commendator Plana, 
nearly in the following terms :—“ A circumstance, with regard 
to the structure of the Milky Way, which forcibly strikes me 
every time I observe the heavens during any of these serene 
and clear nights, as frequent here in summer as they are in 
your lovely Italy, is that the portion of this wonderful zone, 
which lies between Sirius and Antares, is perfectly illuminated 
by the stars, of which a multitude is visible to the naked eye. 
If starting from the centre of this portion we follow its direc- 
tion with the eye towards the north, the illumination gradually 
diminishes until nothing remains but a weak hazy light with- 
out any trace whatsoever of stars. ‘The southern half of the 
Milky Way appears therefore nearer to our solar system than 
the northern half, or in other words, the Milky Way is not 
merely a stratum, but a ring of stars in which the sun is si- 
tuated excentrically, being nearer to the constellation of the 
Cross than to the point diametrically opposite.” 
You will allow me here to recall to you, that the constella- 
tion of the Cross, of which mention is here made, is the same 
that Dante has rendered remarkable by an assertion to which 
too absolute a sense has been given in these lines :— 
“To mi volsi a man destra, e posi mente 
Al? altro polo ; e vidi quattro stelle 
Non viste mai, fuor ch’ alla prima gente *.” 
Purg. canto i. ver. 22. 
« To the right hand I turn’d, and fix’d my mind 
On the other pole attentive; when I saw » 
Four stars ne’er seen before, save by the ken 
Of our first parents.” Cary’s Translation, verse 22. 
The ingenious observation of Sir J, Herschel gives to our 
notion of the milky nebula that completeness which his father, 
who was not acquainted with the southern hemisphere, was 
unable togive. ‘The milky nebula, in accordance with its ap- 
pearance, has therefore the shape of a ring, such as would 
* In the notes commonly appended to the Divina Commedia, the ques- 
tion is frequently mooted, in what way Dante could be informed of the 
principal stars which now form part of the constellation of the Cross, and 
it is supposed that he may have obtained such information from Marco 
Polo, who had crossed the equinoctial line in his travels. This may have 
