From measurements made by Professor Hall, it is found, with a near approach to certainty, that the mass of Mars is equal to 1-3,090,000th part of the mass of the sun. This result was arrived at after only ten minutes of calculation, and is believed to be more nearly accurate than that obtained by M. Le Verrier, the great French astronomer, from observations continued through a century and after several years of laborious calculation by a corps of computers. This wonderful difference in the expenditure of time and labor is due to the vigilance of Professor Hall and to the admirable qualities of his instrument, the great twenty-six inch refracting telescope made by Alvan Clark & Sons. * * * * * Oakland, Cal. DEAR ST. NICHOLAS: I do not wish to make you any trouble, but I would like it very much if you could find room in some number to give a good explanation of the great war in Europe. I can't understand it in the newspaper, but I am pretty sure you can make it plain and simple enough for all of your young readers.--Yours truly, NEB. The Turco-Russian war is partly a conflict of religions and partly one of politics. The Turks came into Europe as the religious emissaries of the Mohammedan religion. In all the provinces of Turkey in Europe which they conquered, the Christians of the Greek, Armenian and Catholic churches were the victims of a bitter persecution. The Czar of Russia is the head of the Greek church. He has made repeated wars in defense of the children of his faith. There have been many wars and long sieges which, like the present, were said to be only in defense of the faith of the Greek church--a crusade and a holy war, But if "Neb" will only look at the map of Russia, he will see, if he will study climate a little, that the vast empire of Russia has one thing lacking. It has no good outlet to the Atlantic Ocean, no power upon the seas. The Baltic Sea is closed half the year by ice. The great wheat trade of Russia concentrates at Odessa, on the Black Sea, and to get her grain to market she must pass through the Turkish lanes of the Bosphorus and the Dardanelles. Russia is a prisoner as to access to the Mediterranean, and so to the Atlantic, and so to the world at large. If she is at war, she cannot float her fleets. If she is at peace, she cannot sell her grain without going roundabout through her neighbors' lots. Turkey stands the tollman at the turnpike-gate, controlling and usurping the highway of all nations.