In his second conjecture, Halley was more fortunate, as indeed might be expected, since it was formed upon more conclusive grounds. He found that the paths of comets which had appeared in 1531 and 1607 were nearly identical, and that they were in fact the same as the path followed by the comet observed by himself in 1682. He suspected, therefore, that the appearances at these three epochs were produced by three successive returns of the same comet, and that, consequently, its period in its orbit must be about seventy-five and a half years. The probability of this conclusion is strikingly exhibited to the eye, by presenting the elements in a tabular form, from which it will at once be seen how nearly they correspond at these regular intervals. ===================================================================== Time.|Inclination of|Long. of the |Long. Per.|Per. Dist. |Course. |the orbit. |node. | | | ===================================================================== 1456 | 17°56´ | 48°30´ |301°00´ | 0°58´ |Retrograde. 1531 | 17 56 | 49 25 |301 39 | 0 57 | " 1607 | 17 02 | 50 21 |302 16 | 0 58 | " 1682 | 17 42 | 50 48 |301 36 | 0 58 | " ===================================================================== So little was the scientific world, at this time, prepared for such an announcement, that Halley himself only ventured at first to express his opinion in the form of conjecture; but, after some further investigation of the circumstances of the recorded comets, he found three which, at least in point of time, agreed with the period assigned to the comet of 1682. Collecting confidence from these circumstances, he announced his discovery as the result of observation and calculation combined, and entitled to as much confidence as any other consequence of an established physical law.