A. MATHEMATICS AND ASTRONOMY. 41 



sphere. The shadow of this point falls upon lines cut into 

 the concave spherical surface, and shows the hour of the day. 

 Three circles are so drawn as to indicate the path described 

 by the shadow of the pencil-point at the time of the equi- 

 noxes and solstices. 



The conical sun-dial is another form known to have been 

 used by the ancient Greeks, but no description of it has been 

 preserved in their scientific literature. Lately, however, a 

 complete copy of such a dial has been discovered. It con- 

 sists of a marble block about two inches thick, whose upper 

 and lower surfaces are horizontal, but one of whose side sur- 

 faces is so cut that it is parallel to the equator, and is itself 

 turned toward the north pole. The inner surface of a right 

 cone is worked into the marble block so that its base stands 

 on the inclined side surface. Its axis is therefore parallel to 

 the earth's axis. The angle at the vertex of the cone is 

 equal to the latitude of the place. Heis* Woche?ischrift, 

 1874,150. 



SCIENTIFIC BALLOONING. 



In a balloon ascent recently made for scientific purposes by 

 Messrs. Croce-Spinelli and Sivel, the authors ascended to a 

 height of about 22,000 feet, experiencing a temperature at that 

 elevation of 7.6 Fahr. Spectroscopic and physiological ob- 

 servations were particularly attended to. It was noted that of 

 the two obscure bands on the right and left hand of the double 

 line D in the solar spectrum, the right-hand band disappear- 

 ed at an elevation of about 16,000 feet, while the left-hand 

 band vanished at about 21,000 feet, thus confirming Janssen's 

 opinion that these bands are of terrestrial origin. The ob- 

 servers carried with them cans of condensed oxygen, and 

 found some relief from the effect of the rarefaction of the air 

 by breathing that gas. 



CHANGES IN THE NEBULA AROUND ETA ARGUS. 



The latest communication in reference to the changes of 

 the nebula surrounding Eta Argus is by Mr. Abbott of Ho- 

 bart -Town, Van Diemen's Land, in which he states that the 

 small stars adjacent to the principal star, though agreeing 

 very closely with drawings made a few years ago, have but 

 little agreement with drawings made in 1836. A very consid- 



