ASTRONOMY. 205 



The diameter of Mars is deduced (for distance 1) to be i>olar diameter 

 = 9".349 ± 0".010 from tlie meau of Arago's, Bessel's, Kaiser's, 

 Main's, and Haiitwig's observations. 



Tlie Strassbiirg observations alone gave polar diameter = 9".311; 

 equatorial diameter = 9.519. 



I\Iauy good drawings of Mars were made in 1877, among which those 

 of Mr, Green, at Madeira, of Mr. Dreyer, and of M. Niesten, at 

 Brussels, deserve especial notice. Mr. Green and Mr. Burton have 

 also observed Mars in 1879. 



[N^either Mr. Green nor any one else in 1877 succeeded in seeing the 

 remarkable long and narrow canals- depicted in Schiaparelli's " Osser- 

 vazioni astronomiche e tisiche suU'asse di rotatione e sulla topografia 

 del pianeta Marte," Eoma, 1878, 4to; * but M. Terby has pointed out that 

 drawings made by Prof. IIolden, at Washington, in 1875, contain these 

 canals, and that thus their subsequent discovery by M. Schiaparelli 

 in 1877 is fully verified. This paper, published towards the end of 

 1878, contains first a new determination of the direction of the axis of 

 rotation, the measures being made by placing the micrometer wire tan- 

 gent to the middle of the snow spot. The results were, for September 



27-0. 



Areocentr. Long. { of centre 29-0460-1-1 -0077. 



" Polar Dist. S of spot, G-147-J-U-123. 



Geocentr. Angle of Pos. of Axis, 1G4-90-J-0.10. 



The second chapter contains the determination of the areographio 

 position of sixty-two principal i^oints on the surface. From this an 

 exact map on Mercator's projection has been constructed, but as only 

 two colors are used, blue and white, to represent dark and bright, and 

 no shading at all is given, it is rather difficult to compare this mnp with 

 others. The innumerable "canals," which in all directions cross the 

 map, increase this difficulty. Four representations of the disk in ortho- 

 graphic projection (Table V), founded on all the drawings made at 

 Milan, are very much more adapted to be compared with other maps. 



One of the most important publications of the year is the eleventh 

 volume (Part I) of the "Annals of the Observatory of Harvard Col- 

 lege," containing Professor Pickering's Photometric Observations 

 made with the 15-inch refractor. The author first made experiments 

 with a Zollner's i)hotometer and other instruments in which the star is 

 compared with an artificial light, but on account of the want of simi- 

 larity between the real and the artificial star, and the difficulty of ap- 

 plying a correction for changes in opacity of the air, which only aflect 

 the real star, the use of a lamp was abandoned, and all comparisons 

 were made with some bright star in the vicinity of the object observed. 

 All variations in the condition of the air were thus eliminated, both ob- 

 jects being equally affected by it. To insure a comparison free from 



* Of this remarkable work a German translation is about to appear. M. O. Stru\te 

 bas given a very full account of it in the Vierteljabrsscbriit dcr Astrouomiscben 

 Gesellscbaft, XIV, p. 22-39 (1879). 



