46 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



chased. This last is the result of thirty-four years' work, 

 and contains about 34,000 craters and an equal number of 

 hills, besides other objects. It is to be explained by a suita- 

 ble text. Work upon Birt's map, formerly prosecuted by aid 

 of the British Association's funds, is for the present suspend- 

 ed. It is to be hoped that this may one day be completed. 

 12^, Jfy 18, 1876. 



SUPPOSED OBSERVATION OP AN INTER-MERCUEIAL PLANET. 



M. Weber, of Peckeloh, observed on the 4th of April, 1876, 

 about 4*^, a round spot on the sun which was not there on the 

 morning of that day, and which had disappeared on the morn- 

 ing of the 5th. It is somewhat curious, as pointed out by Dr. 

 Wolf, of Zurich, who communicates the observation to Le 

 Yerrier, that this observation is 6219 days rr 148 x 42.02 days 

 after that of Lescarbault, as 42 days seems to be the period 

 indicated by former observations (?) of this supposititious 

 planet. Thus the observations of Steinhiibel (1820), Pons 

 (1823), Stark (1826), Capocci (1845), Schmidt (1847), Ohrt 

 (1857), and Lescarbault (1859), seem to indicate a period of 

 42 days, the separate results ranging from 42.07 to 41.95. 

 From Lescarbault's observation alone Le Verrier deduced a 

 period of about 19 days. 6 B, Aug. 28, 1876, 510. 



GLASS DIVIDED CIRCLES FOR THE MEASUREMENT OF ANGLES. 



Mr. Lewis M. Rutherfurd publishes in the American Jour- 

 nal of Scieiice iov Awgw&i^ 1876, an account of a circle divided 

 on glass which he has had fitted to his sj^ectrometer. It is 

 ten inches in diameter, divided to ten minutes of arc, and 

 read by two microscopes magnifying seventy-five diameters 

 to single seconds. A second on such a circle is about one 

 forty-thousandth of an inch, but such was the fineness of 

 the lines of division that the probable accidental error of 

 pointing was considerably less than half a second of arc. 

 Mr. Rutherfurd is of the opinion tliat on glass circles so 

 divided and of fifteen inches in diameter, more accurate work 

 could be done than upon the metal circles (thirty-six inches 

 and upward in diameter) now in use in large astronomical 

 instruments. " The advantages of this system are obvious : 

 perfection of surface, permitting a line of any desired fine- 

 ness; facility of illumination, permitting the extension of the 



