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136 When he had proceeded some way in his inquiries, he received from a friend a copy of a catalogue of eighty stars made by Mayer of Göttingen in 1756, "and compared with the same stars as given by Roemer in 1706." Both Roemer and Mayer were men of the highest ability. Previously he knew this catalogue only in an extract which he found in a French book on astronomy. Setting to work on the new material thus furnished, and laying aside thirteen or fourteen of the stars as those he had already examined, he separated the others into two classes, those which went for his view of a motion of the sun through space, and those whose motions "must be ascribed to a real motion in the stars themselves" Mayer, admirable astronomer though Herschel admitted him to be, did not countenance the idea of a motion of the sun with all its planets through space. "Were it so," he wrote in 1760, "were the sun and all the planets and our home, the earth, advancing towards some quarter, all the stars in that part of the heavens would seem to open out, and those in the opposite quarter to come together, just as, when you are walking through a wood, the trees which are in front of you seem to separate from each other, and those which are behind to draw closer." Herschel, seizing on Mayers illustration of trees in a wood, declared that these very changes were taking place among stars in the heavens. At the same time he was encouraged by a short tract sent him by the author. Dr. Alexander Wilson, Professor of Astronomy at Glasgow, and printed in 1777, entitled Thoughts on General Gravitation and Views thence arising as to the State of the Universe. A friendship sprang up