Yet few people ask from books what books can give us. Most commonly we come to books with blurred and divided minds, asking of fiction that it shall be true, of poetry that it shall be false, of biography that it shall be flattering, of history that it shall enforce our own prejudices. If we could banish all such preconceptions when we read, that would be an admirable beginning. Do not dictate to your author; try to become him. Be his fellow worker and accomplice. If you hang back, and reserve and criticize at first, you are preventing yourself from getting the fullest possible value from what you read. But if you open your mind as widely as possible, then signs and hints of almost imperceptible fineness, from the twist and turn of the first sentences, will bring you into the presence of a human being unlike any other. Steep yourself in this, acquaint yourself with this, and soon you will find that your author is giving you, or attempting to give you, something far more definite.
。式中的G为万有引力恒量，M为地球质量，m为物体的质量，r为物体到地心的距离，并以无限远处的引力势能为零势能。一颗质量为m的地球卫星，在离地高度为H处环绕地球做匀速圆周运动。已知地球的半径为R，地球表面的重力加速度为g，地球质量未知。试求：