From what has been said it will be apparent that Mercury is scarcely so interesting a telescopic object as some of the other planets. Small instruments are practically ruled out of the field by the diminutive size of the disc which has to be dealt with, and the average observer is apt to be somewhat lacking in the patience without which satisfactory observations of an object so elusive cannot be secured. At the same time there is a certain amount of satisfaction and interest in the mere detection of the little sparkling dot of light in the Western sky after the sun has set, or in the Eastern before it has risen; and the revelation of the planet's phase, should the telescope prove competent to accomplish it, gives better demonstration than any diagram can convey of the interior position of this little world. It is consoling to think that even great telescopes have made very little indeed of the surface of Mercury. Schiaparelli detected a number of brownish stripes and streaks, which seemed to him sufficiently permanent to be made the groundwork of a chart, and Lowell has made a remarkable series of observations which reveal a globe seamed and scarred with long narrow markings; but many observers question the reality of these features altogether. It is perhaps just within the range of possibility that, even with a small instrument, there may be detected that blunting of the South horn of the crescent planet which has been noticed by several reliable observers. But caution should be exercised in concluding that such a phenomenon has been seen, or that, if seen, it has been more than an optical illusion. Those who have viewed Mercury under ordinary conditions of observation will be well aware how extremely difficult it is to affirm positively that any markings on the surface or any deformations of the outline of the disc are real and actual facts, and not due to the atmospheric tremors which affect the little image. Interesting, though of somewhat rare occurrence, are the transits of Mercury, when the planet comes between us and the sun, and passes as a black circular dot across the bright solar surface. The first occasion on which such a phenomenon was observed was November 7, 1631. The occurrence of this transit was predicted by Kepler four years in advance; and the transit itself was duly observed by Gassendi, though five hours later than Kepler's predicted time. It gives some idea of the uncertainty which attended astronomical calculations in those early days to learn that Gassendi considered it necessary to begin his observations two days in advance of the time fixed by Kepler. If, however, the time of a transit can now be predicted with almost absolute accuracy, it need not be forgotten that this result is largely due to the labours of men who, like Kepler, by patient effort and with most imperfect means, laid the foundations of the most accurate of all sciences.