Yet for the last ten—we might, with more truth, say for fifty—years back, the best astronomers have been preparing to observe, with unequalled care, the passage of that little black spot. Some have again and again gone over the records of the observations made in 1761 and 1769, when it was last seen, criticising what was then done, distinguishing what was well done from what they judge to have been faulty, and tracing these faults back to their sources—either to the imperfection of the instruments used, to personal errors, or to mistakes or omissions of the observers themselves. In the observations now to be made, all these sources of error will, as far as possible, be excluded. Others have spent years in patiently going over the long calculations connected with those observations, detecting and eliminating any errors they find, and introducing such corrections as the subsequent advance of astronomical science demands. The amended results thus obtained are ready for comparison, at their proper value, with the additional and, it is hoped, better results to be obtained from the observations of next December. Still others have used, and are now using, their utmost skill in constructing instruments of hitherto unequalled excellence for the great occasion. Besides great improvements in the instruments known in 1769, they have devised others, perhaps more valuable, and of a character then not dreamed of. Others, again, have devoted months to the nicest and most intricate calculations of the movements of the earth and the planets, in order to know in full time beforehand what special stations on the surface of the earth will, that day and at the required hours, afford the most eligible positions from which to make the desired observations.