If the bomber wished to blow up a wall, he was told how to compute by simple mathematics the quantity of explosive required. A bridge “will require twice the charge needed for a wall”--and the vulnerable points of the bridge were indicated. Telephone and telegraph poles and wires, street gratings, street railways, locomotives, steam-boilers, all came in for their share of attention. “It is very easy to find suitable receptacles for bombs,” the writer went on. “For example, large inkwells, brass handles such as are used on letter-presses.... For certain purposes a bottle may be made to serve as a bomb--they are suitable for throwing from a window.... Fragile glass bottles when filled with this solution (an incendiary mixture) make handy incendiary bombs to hurl among troops, official gatherings, etc.; also to pour from windows upon troops, or to throw from a drinking glass or pail....” I have wondered whether Gavrio Prinzip of Sarajevo ever saw this book, and whether it may not have been translated into Italian from the original German. Mere possession of this wicked treatise would suggest that the owner was up to no good, especially if the owner, as in this case, was known to be a volatile member of an anarchistic circle who had already declared his intentions of wrecking something. It was reasonable to assume that there must be such a book of instruction in existence, that the bombers had not been handling delicate explosives with no better knowledge than word-of-mouth, hearsay chemistry, but I am free to confess that my first sight of the pamphlet brought the plots of the men we were watching very close to grim reality. I never knew just when we would get an ambulance call and have to go and pick Polignani out of the wreck of a premature explosion, and I never heard him report in on the telephone that I didn’t experience a momentary apprehension of his latest news. The detective himself was calm enough, and enthusiastic over the fact that the trail was growing hotter all the time. The question of evidence of the previous explosions was in the background now, and the activities of the Brescia Circle as a political unit did not concern us nearly as much as the activities of three of its members with their “andimonio, collorate di potase” and their pamphlet, and their hatred of the Catholic Church. Polignani had seen this hatred demonstrated many times by Carbone. They passed two Sisters of Charity one chilly evening near the Harlem station, and the anarchist spat, and cursed them. So the detective was not surprised by Abarno’s proposal on the night of St. Valentine’s Day that the three conspirators plant their bombs in St. Patrick’s Cathedral. “We’ll go over there some day soon and look for a good place to set them. And then we’ll plant the bomb on some good holiday--say on March 21, eh?” “What’s that day?” Polignani inquired. “The Commune!” Abarno answered.