The most valuable books in the collection were four. There was a Hebrew chronicle under the title of _Zemach David_,[14] written by a sensible chief rabbi in Prague, named Rabbi David Gans. He was also the author of the astronomical book spoken of in the sequel, and he had had the honour of being acquainted with Tycho Brahe, and of making astronomical observations with him in the Observatory at Copenhagen. There were besides, a Josephus, which was evidently garbled, and a History of the Persecutions of the Jews in Spain. But what attracted me most powerfully was an astronomical work. In this work a new world was opened to me, and I gave myself up to the study with the greatest diligence. Think of a child about seven years of age, in my position, with an astronomical work thrown in his way, and exciting his interest. I had never seen or heard anything of the first elements of mathematics, and I had no one to give me any direction in the study: for it is needless to say, that to my father I dared not even let my curiosity in the matter be known, and, apart from that, he was not in a position to give me any information on the subject. How must the spirit of a child, thirsting for knowledge, have been inflamed by such a discovery! This the result will show. As I was still a child, and the beds in my father's house were few, I was allowed to sleep with my old grandmother, whose bed stood in the above-mentioned study. As I was obliged during the day to occupy myself solely with the study of the Talmud, and durst not take another book in my hand, I devoted the evenings to my astronomical inquiries. Accordingly after my grandmother had gone to bed, I put some fresh wood on the fire, made for the cupboard, and took out my beloved astronomical book. My grandmother indeed scolded me, because it was too cold for the old lady to lie alone in bed; but I did not trouble myself about that, and continued my study till the fire was burnt out. After I had carried this on for some evenings, I came to the description of the celestial sphere and its imaginary circles, designed for the explanation of astronomical phenomena. This was represented in the book by a single figure, in connection with which the author gave the reader the good advice, that, since the manifold circles could not be represented in a plane figure except by straight lines, he should, for the sake of rendering them more clearly intelligible, make for himself either an ordinary globe or an armillary sphere. I therefore formed the resolution to make such a sphere out of twisted rods; and after I had finished this work, I was in a position to understand the whole book. But as I had to take care lest my father should find out how I had been occupied, I always hid my armillary sphere in a corner behind the cupboard before I went to bed.