finds a similar difficulty in connection with the stars and
nebulas. It is an impossibility to regard these objects as new;
they must be as old as the universe itself. They radiate heat and
light year after year. In all probability, they must have been
doing so for millions of years. Whence comes the supply? The
geologist may well claim that until the astronomer explains this
mystery in his own domain, he cannot declare the conclusions of
geology as to the age of the earth to be wholly inadmissible.

Now, the scientific experiments of the last two years have brought
this mystery of the celestial spaces right down into our earthly
laboratories. M. and Madame Curie have discovered the singular
metal radium, which seems to send out light, heat, and other rays
incessantly, without, so far as has yet been determined, drawing
the required energy from any outward source. As we have already
pointed out, such an emanation must come from some storehouse of
energy. Is the storehouse, then, in the medium itself, or does the
latter draw it from surrounding objects? If it does, it must
abstract heat from these objects. This question has been settled
by Professor Dewar, at the Royal Institution, London, by placing
the radium in a medium next to the coldest that art has yet
produced--liquid air. The latter is surrounded by the only yet
colder medium, liquid hydrogen, so that no heat can reach it.
Under these circumstances, the radium still gives out heat,
boiling away the liquid air until the latter has entirely
disappeared. Instead of the radiation diminishing with time, it
rather seems to increase.

Called on to explain all this, science can only say that a
molecular change must be going on in the radium, to correspond to