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other satellites. On the contrary, Herschel distinctly says that he had not 
kept hack the announcement on account of any doubts he had, but because 
he hoped to determine the elements of the orbits. Now it has never hap- 
pened that where Sir William Herschel has expressed certainty about a 
matter of observation, he has been shown eventually to have been in error. 
But it may be urged that Mr. Lassell’s telescope being far finer than Herschel’s, 
and showing the four other satellites far more distinctly than they seem to 
have been seen by Herschel, the non-detection of the four fainter ones would 
seem to show that they have no existence. Here, however, a distinction 
must be drawn between two qualities of a telescope — defining and illumi- 
nating power. It is quite clear that as respects defining power Mr. Lassell’s 
four-feet reflector has greatly the advantage over the four-feet reflector at 
Slough ; and as respects the satellites nearest to the planet, he would on 
this account alone probably have a certain advantage, since an ill-defining 
reflector would throw a good deal of diffused light over the field near the 
planet. In illuminating power, however, it seems by no means so clear that 
the Slough reflector is greatly surpassed by Mr. Lassell’s, even under equal 
circumstances. Now Sir William Herschel failed to detect the satellites when 
he used his telescope as Mr. Lassell has always used his — that is, as a New- 
tonian ; and only when he used the u front view,” by which the illuminating 
power was greatly increased, could he gain even a glimpse of them. Even 
then only his skill and long practice in searching for minute points of light 
enabled him (as he himself tells us) to succeed. Under these circumstances 
there seems no adequate reason for dismissing these four satellites from the 
solar system. It is worthy of notice that Mr. Lassell does not seem to have 
been aware, when he urged the dismissal of the satellites, that Herschel 
had had more than a suspicion of them ; for he says “ Herschel may have 
mistaken small stars for satellites,” the very error the great astronomer was 
so careful to avoid. So far as one of the satellites in question is concerned, 
indeed, Mr. Lassell has himself shown (unwittingly) that it may exist. 
For he has said that if any satellites within the range of his telescope 
exist, they must travel very far from their primary, and in a period of at 
least three months. Now one of Herschel’s is at a distance corresponding to 
a period of more than 3^- months. 
Photographing a Solar Prominence by Means of the Spectroscope . — Pro- 
fessor Young has succeeded in taking a photograph of a solar prominence by 
means of a double-acting spectroscope of high dispersive power. The result 
is in itself, as he admits, valueless; but it is full of promise. The day will 
doubtless come when the condition of the sun’s limb will be recorded as 
systematically by photography as the condition of the solar surface has been 
recorded at the Kew observatory. 
The Planets . — Jupiter will continue favourably situated for observation 
during the next quarter. He is stationary on February 10, and in quadra- 
ture on March 8. Mars, however, is the planet of the quarter, as he comes 
to opposition on March 20. He will be stationary on February 9. As he will 
be in aphelion on January 21, this is not a favourable conjunction. But the 
northern parts of his surface ought now to be studied, as they are more fully 
turned towards the earth than in perihelion oppositions. Saturn is slowly 
