the iron wire would have been fused into drops of liquid, the current would have been broken, and the lamp would have been destroyed.  Nor would the attempt to make an incandescent lamp have proved much more successful had the filament been made of any other metal.  The least fusible of metals is the costly element platinum, but even a wire of platinum, though it would stand much more heat than a wire of iron or of steel, would not have retained the solid form by the time it had been raised to the temperature necessary for an incandescent lamp.

There is no known metal, and perhaps no substance whatever, which demands so high a temperature to fuse it as does the element carbon.  A filament of carbon, and a filament of carbon alone, will remain unfused and unbroken when heated by the electric current to the dazzling brilliance necessary for effective illumination.  This is the reason why this particular element is so indispensable for our incandescent electric lamps.  Modern research has now taught us that, just as the electrician has to employ carbon as the immediate agent in producing the brightest of artificial lights down here, so the sun in heaven uses precisely the same element as the immediate agent in the production of its transcendent light and heat.  Owing to the extraordinary fervor which prevails in the interior parts of the sun, all substances there present, no matter how difficult we may find their fusion, would have to submit to be melted, nay, even to be driven off into vapor.  If submitted to the heat of this appalling solar furnace, an iron poker, for instance, would vanish into invisible vapor.  In the presence of the intense heat of the inner parts of the sun, even carbon itself is unable to remain solid.  It would seem that it must assume a gaseous form under such circumstances, just as the copper and the iron and all the other substances do which yield more readily than it to the fierce heat of their surroundings.

The buoyancy of carbon vapor is one of its most remarkable characteristics.  Accordingly immense volumes of the carbon steam in the sun soar at a higher level than do the vapors of the other elements.  Thus carbon becomes a very large and important constituent of the more elevated regions of the solar atmosphere.  We can understand what happens to these carbon vapors by the analogous case of the familiar clouds in our own skies.  It is true, no doubt, that our terrestrial clouds are composed of a material totally different from that which constitutes the solar clouds.  The sun evaporates the water from the great oceans which cover so large a proportion of our earth.  The vapor thus produced ascends in the form of invisible gas through our atmosphere, until it reaches an altitude thousands of feet above the surface of the earth.  The chill that the watery vapor experiences up there is so great that the vapor collects into little liquid beads, and it is, of course, these liquid beads, associated in countless myriads, which form the clouds we know so well.