A. MATHEMATICS AND ASTRONOMY. 57 



SPECTEOSCOPIC DIAMETEK OF THE SUX. 



At the recent meeting of Italian astronomers, experiments 

 were made by Secclii, Tacchini, Rayet, and Dorna to deter- 

 mine the difterence between the diameter of the sun as deter- 

 mined by the spectroscope and by the method of meridian tran- 

 sits. From the observations of ten days the spectroscopic 

 semi-diameter was less than the transit semi-diameter by 

 0.124", and less than the Nautical Almanac semi-diameter by 

 0.104". Atmospheric conditions were found to be influential 

 in these determinations. 2 G, November^ 1875, 118. 



IDENTIXr OF COMET VII., 1873 (cOGGIa), WITH COMET I., 



1818 (pons). 



Dr. Weiss, of the Vienna Observatory, has investigated the 

 orbit of the comet discovered by Coggia the 10th of Novem- 

 ber, 1873. As he has previously shown, there is scarcely a 

 doubt that this comet is identical with the comet discovered 

 by Pons in 1818, and in this case the determination of the 

 period of revolution is quite important. Dr. Weiss finds that 

 there are three possible periods, viz., 55.82 years, 18.61 years, 

 and 6.20 years. Of these three, the second is the least prob- 

 able ; and of the first and third. Dr. Weiss considers the 

 period of 6.20 years the most probable for the present, al- 

 though his computations are to be carried farther as soon as 

 he shall have received further observations of this body dur- 

 ing its last appearance. 38 6^, No. 2072. 



A NEW MERIDIAN INSTRUMENT AT THE OBSERVATORY AT 



RIO. 



M. Liais, Director of the Observatory of Rio, describes a 

 new arrangement of his mural circle (made by DoUond), 

 which is intended to convert it into an instrument suitable 

 for determining right ascensions. Within the tube of the 

 mural-circle telescope, M, is fixed a plane mirror, which is 

 perpendicular to the axis of rotation of the mural circle. At 

 ten feet from the circle, and looking toward it, is a telescope 

 with high magnifying power, A. Close to A is a mark 

 {inire) which can be moved either vertically or horizontally 

 by means of two micrometer screws of known value. If M 

 is in any given position, the mark can be })laced, by means of 



C 2 



