1876.] Encouragement of Scientific Research, 483 
relatively light mineral as olivine, appeared the more to be 
incompatible with igneous fusion the more one became 
acquainted with what occurs in our furnaces. In the case 
of a melted mass of metallic iron and slag the separation is 
all but complete, and no such thing as an uniform mixture 
is to be found. For a long time this circumstance remained 
a puzzle ; but in walking out in the country one summer 
evening, some trivial circumstance, long since forgotten, led 
me to perceive that the almost immediate separation of the 
metal and the slag was due to the powerful attraction of our 
earth, and that in any situation where the force of gravita- 
tion was very weak no such separation would occur. The 
general conclusion then became very simple. Meteoric 
masses of iron and olivine must have cooled from a state of 
fusion either as small masses in free space, or near the 
centre of large planets.” 
One more instance may be quoted, drawn from a different 
sphere of research “ For many years, in common with all 
who had studied the subject, I had referred the position of 
the absorption-bands seen in the speCtra of different colour- 
ing matters to an artificial scale, or, in a few instances, to 
the principal Fraunhofer lines. One day, however, whilst 
rambling over the quiet hills of Derbyshire it occurred to 
me, apparently quite accidentally, that such a system had 
no physical foundation, and that the time method was to 
express the position of all parts of the spedtrum in terms of 
the wave-lengths of the light at each part. I at once set to 
work to contrive the means of doing this conveniently, and 
it was not long before I succeeded.” “ It would be easy to 
multiply such examples and to show the manner in which 
one train of ideas led to another. Very often the circum- 
stances and train of ideas which led to a discovery were 
immediately forgotten in the face of the result, like the 
scaffolding used in the eredtion of some stately building, and 
sometimes the circumstances were connected with the main 
question in a manner so ridiculous that it would be altogether 
inappropriate to describe them.” 
From these cases we may surely infer that for the suc- 
cessful prosecution of research abundant and uninterrupted 
time is one of the main requisites ; time not merely for 
adtual thought, but leisure. It will at once strike the 
reader that in all the cases given by Mr. Sorby the happy 
thought occurred to him during gentle exercise and when 
the mind was perfectly at ease. This we can confirm, both 
from our individual experience and from the statements of 
friends. But what^ then^ is the case of a person who has no 
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