the world in less than fifteen hours. Each of the mammoth guns will be a trifle over fifty-three feet in length and the estimated cost of each will be $85,000. Judging from the performance of the twelve-inch guns it is figured that these greater weapons should be able to deliver three shots a minute. If all ten guns of either of the projected _Dreadnoughts_ should be brought into action at one time and maintain the three shot rapidity for one hour, the cost of the ammunition expended in that hour would reach the enormous sum of $2,520,000. Very few, however, of the big guns are called upon for the three shots a minute rate, for the metal would not stand the heating strain. The big guns are expensive and even when only moderately used their "life" is short, therefore, care is taken not to put them to too great a strain. With the smaller guns it is different. Some of six-inch bore fire as high as eight aimed shots a minute, but this is only under ideal conditions. Great care is being taken now to prolong the "life" of the big guns by using non-corrosive material for the charges. The United States has adopted a pure gun-cotton smokeless powder in which the temperature of combustion is not only lower than that of nitro-glycerine, but even lower than that of ordinary gunpowder. With the use of this there has been a very material decrease in the corrosion of the big guns. The former smokeless powder, containing a large percentage of nitro-glycerine such as "cordite," produced such an effect that the guns were used up and practically worthless, after firing fifty to sixty rounds. Now it is possible for a gun to be as good after two or even three hundred rounds as at the beginning, but certainly not if a three minute rate is maintained. At such a rate the "life" of the best gun made would be short indeed. CHAPTER XV MYSTERY OF THE STARS Wonders of the Universe--Star Photography--The Infinity of Space. In another chapter we have lightly touched upon the greatness of the Universe, in the cosmos of which our earth is but an infinitesimal speck. Even our sun, round which a system of worlds revolve and which appears so mighty and majestic to us, is but an atom, a very small one, in the infinitude of matter and as a cog, would not be missed in the ratchet wheel which fits into the grand machinery of Nature.