The next question to be considered is in what direction we may expect the greatest advance in astronomy will be made.  Fortunate indeed would be the astronomer who could answer this question correctly.  When Ptolemy made the first catalogue of the stars, he little expected that his observations would have any value nearly two thousand years later.  The alchemists had no reason to doubt that their results were as important as those of the chemists.  The astrologers were respected as much as the astronomers.  Although there is a certain amount of fashion in astronomy, yet perhaps the best test is the judgment of those who have devoted their lives to that science.  Thirty years ago the field was narrow.  It was the era of big telescopes.  Every astronomer wanted a larger telescope than his neighbors, with which to measure double stars.  If he could not get such an instrument, he measured the positions of the stars with a transit circle.  Then came astrophysics, including photography, spectroscopy and photometry.  The study of the motion of the stars along the line of sight, by means of photographs of their spectra, is now the favorite investigation at nearly all the great observatories of the world.  The study of the surfaces of the planets, while the favorite subject with the public, next to the destruction of the earth by a comet, does not seem to appeal to astronomers.  Undoubtedly, the only way to advance our knowledge in this direction is by the most powerful instruments, mounted in the best possible locations.  Great astronomers are very conservative, and any sensational story in the newspapers is likely to have but little support from them.  Instead of aiding, it greatly injures real progress in science.

There is no doubt that, during the next half century, much time and energy will be devoted to the study of the fixed stars.  The study of their motions as indicated by their change in position was pursued with great care by the older astronomers.  The apparent motions were so small that a long series of years was required and, in general, for want of early observations of the precise positions of the faint stars, this work was confined mainly to the bright stars.  Photography is yearly adding a vast amount of material available for this study, but the minuteness of the quantities to be measured renders an accurate determination of their laws very difficult.  Moreover, we can thus only determine the motions at right angles to the line of sight, the motion towards us or from us being entirely insensible in this way.  Then came the discovery of the change in the spectrum when a body was in motion, but still this change was so small that visual observations of it proved of but little value.  Attaching a carefully constructed spectroscope to one of the great telescopes of the world, photographing the spectrum of a star, and measuring it with the greatest care, provided a tool of wonderful efficiency.  The motion, which sometimes amounts