unexpected and puzzling phenomenon appeared. There was trouble in the astronomical world. The fault was generally thrown on the instruments. But whatever the cause of the mishap, there was some room for consolation. They would soon have another opportunity, and might make another trial. In 1769, only eight years off, there would be another transit, and by that time some means would certainly be devised for escaping the evil. In 1769, the stations were as numerous, the governmental aid fully as great, the instruments, they said, more perfect, and the observers, we may be sure, as earnest and as careful as before. Perhaps they were more skilful because of their previous experience. But again all in vain. The same evil reappeared. The resulting uncertainty was even greater. It was held to reach fully twenty seconds. When they undertook to calculate, from such observations, the distance of the sun, some made it not more than 87,890,780 miles, while, according to others, it reached 108,984,560 miles, the majority finding intermediate values. On the whole, it did not appear that there was much improvement on the estimate made by Cassini a century and a half before, that it was not less than 85,000,000 miles. Again and again were the records of the observations studied, scrutinized, and weighed, and the calculations based on them repeated and criticised. Finally, in 1824, Encke, after several years of special study of them, summed all up, and gave, as the best result attainable, 95,274,000 miles. The scientific world, hopeless of anything better, seemed for a time to acquiesce. Some even upheld the estimate of Encke as “so successfully determined as to leave no sensible doubt of its accuracy.” But, despite this, its accuracy has since been impugned, and on very strong grounds. It was known that light travels from the sun to the earth in about 8 minutes 13 seconds. Experiments carefully and ingeniously made by Arago, Foucault, and Fizeau show that light travels with a velocity of nearly 186,000 miles a second. This would give the distance of about 91,400,000 miles. The irregularities of the moon and of Mars have been studied out and calculated on the theory of interplanetary attraction modifying the attraction of the sun. Though the results vary somewhat, yet they all tend in the same direction. Leverrier found 91,759,000 miles; Hansen, the Dane, found 91,659,000 miles; Airey, the Astronomer‐Royal of England, whose earlier opinion of Encke’s estimate we quoted above, has changed his opinion, and now proposes 91,400,000 miles.