A. MATHEMATICS AND ASTRONOMY. 31 



In a second memoir on the same subject, Andre describes 

 experiments made in a dark room with a telescope of OJO"" 

 aperture (1.24'^ focal length), which was diaphragmed down 

 to 0.0 17'". His observations were made on an illuminated 

 slit in a plate of copper, which could be made to appear 

 bright on a dark ground or dark on a bright ground. He 

 also measured the distance between the borders of two such 

 slits lighted from behind, and separated by about the width 

 of each of them. In the first case the difference of the diam- 

 eters observed was 15.82" for an aperture of O.Ol'?'", and 6.16" 

 for one of 0.049, and this difference calculated was 15.68" 

 and 5.33". [O C = -f 0.14", and + 0.83".] In the second 

 case the differences between observation and calculation 

 were O - C - 0.78", + 0.39". 



Andre mentions among the consequences of this law two 

 of immediate importance in the reduction of the French ob- 

 servations : First, the differences of longitude determined by 

 the transits of the moon's limbs (first and second) may vary 

 by so much as 3.5^ of time, when the longitudes are deter- 

 mined by transit instruments of the size furnished to the French 

 parties. Second, in the occultations observed at Greenwich, 

 discussed by Breen, and used by Newcomb to determine the 

 coefiicient of parallactic inequality, a correction of + 1.1" is 

 applied to the lunar diameter, in order to take account of 

 the increase of the moon's diameter by irradiation. 



Andre is of opinion that this correction should not be ap- 

 plied, and that consequently Newcomb's value of the solar 

 parallax from this datum (8.444") should be diminished by 

 0.07"; and he expresses his belief that the results of the late 

 transit of Venus will give a value of the solar parallax at 

 least as trustworthy as those derived by other methods, pro- 

 vided a suitable selection of the best observations is made, 

 that selection to be based on proper physical discussions. 

 6 B, 1876, 3Iarch 13, 607. 



AX AXCIENT DISCOVERY OF A VARIABLE STAR. 



Beaudet calls the attention of the Academy of Sciences of 

 Paris to the fact that among the rare pieces of apparatus in 

 the collection of the Bureau of Arts and Machinery, there is 

 a celestial globe dated 1622, constructed by W. J. Blaen, of 

 Amsterdam. This geographer was originally a student of 



