A is one that undergoes a change in brightness. With some stars the change is as great as four or even six , while with others it may be only one mag… - Caroline Furness

At the we met , the Director, but were especially pleased to see who had made suck a name for herself by her work on . She was in charge of the reduction of the Paris astrographic plates, and we were interested to compare her computing bureau with the one at . She offered to escort us to to visit the venerable , and invitation which we were delighted to accept. We were charmed with picturesque dwelling, made from the stables of the old chateau, with its low-ceiled rooms and quaint winding passages. They made a fascinating setting for the indomitable old Frenchman, who in spite of his eighty years, was planning to make another ascent of that summer, even if he had to be carried to the summit in a chair. He also asked many questions about the college in America where young girls studied mathematical astronomy.

At the present time we employ a for making certain observations which can best be made then, and for other work which is not possible at another time. The most important work, and one which demands the coöperation of at widely distant places, is the observation of s. These occur at other times, but only the brighter stars can be followed to the and such stars are not frequent in its path. During an eclipse, however, stars down to the eleventh are easily followed until they disappear, and any star whose position is accurately determned is available. If an Observatory has undertaken the investigation of the Moon's place, it takes advantage of a total eclipse and prepares a list of stars which are to be occulted at other distant observatoreis, and sends a circular requesting observations. Such a circular was issued by the , Russia, for the eclipse of March 10th. The time of an occultation is much less difficult to determine than a contact of an eclipse. The Moon has no atmosphere, so that the star disappears instantaneously.

did not accept the but evolved one of his own in which he makes the planets revolve about the Sun, but the Sun carries them with itself about the Earth. Part of his observations he reduced himself, publishing among other things a book on the , one on comets, and one on the lunar theory, and an important star catalogue. He had planned several other valuable works, but his early death cut short his projects. He was the first to perceive the importance of applying refraction to observations. He improved the values of the Sun's and Moon's , he discovered two variations in the Moon's longitude in addition to those already known, and one in latitude. In short he improved many values which depended on accurate observation for their determination.