The friendship between George Ellicott and Banneker grew stronger as the years went by, and their common interests in mathematics and natural science led to a fellowship which often brought them together. This interest led George Ellicott to lend Banneker a number of mathematical books and instruments. Among these books were Mayer's _Tables_, Ferguson's _Astronomy_ and Leadbetter's _Lunar Tables_. When these books and instruments were handed to Banneker it was Ellicott's intention to remain there a while to give Banneker some personal instruction in the use of them, but he was prevented by lack of time from carrying out this intention. On calling again on Banneker shortly afterward, to offer him this instruction, Ellicott was surprised to find that Banneker had already discovered for himself the key to the use of both and was "already absorbed in the contemplation of the new world which was thus opened to his view."[163] They had literally made him fix his gaze on the stars, for the study of astronomy thus became his one absorbing passion. He had now nearly covered his three score years, and it was no little tribute to his mental vigor that he should have determined at that age to master so abstruse a science as astronomy. But by degrees he gave himself up to its study with unusual zeal. His favorite method of studying this science was to lie out on the ground at night, gazing up at the heavens till the early hours of the morning. He then tried to restore his tired mind and body by sleeping nearly all the next day. This habit nearly caused him to fall into disrepute among his neighbors, who, ignorant of his plans, accused him of becoming lazy in his old days. In 1789 he had advanced so far with his plan as to project a solar eclipse, the calculation of which he submitted to his friend George Ellicott. In the study of these books Banneker detected several errors of calculation, and, writing to his friend Ellicott, he made mention of two of them. On one occasion he wrote: "It appears to me that the wisest men may at times be in error; for instance, Dr. Ferguson informs us that, when the sun is within 12 deg. of either node at the time of full, the moon will be eclipsed; but I find that, according to his method of projecting a lunar eclipse, there will be none by the above elements, and yet the sun is within 11 deg. 46' 11" of the moon's ascending node. But the moon, being in her apogee, prevents the appearance of this eclipse." And again he wrote Ellicott: