lxiv GENERAL SUMMARY OF SCIENTIFIC AND 



and consequently touch at all points. Of the four radii of 

 curvature present, the first is +5.27 lines, the second +10 

 lines, the third +2.9 lines, and the fourth 5.73 lines. The 

 sign plus refers to curves having the convexity toward the 

 eye of the observer. This eye-piece has been constructed 

 by Steinheil, and is sensibly aplanatic and achromatic, with 

 a field of about thirty degrees. 



Merz has described a new telescope which he has just 

 completed for the observatory at Quito. It has a clear aper- 

 ture of 9 Paris inches, and a focal distance of 116.75 inches. 

 The position circle is divided directly to five minutes, and 

 reads with a vernier to one minute. A double-rino* microm- 

 eter and a filar micrometer are attached, the latter having 

 eight eye-pieces, magnifying respectively 105, 160, 245, 350, 

 455, 585, 780, and 910 diameters. The hour circle is 18 inch- 

 es in diameter, and the declination circle 20 inches; the for- 

 mer is divided to one minute, and reads to two seconds of 

 time ; the latter is divided to five minutes, and reads to 

 four seconds. A number of improvements in the mounting 

 are noticed. 



Payet has published a paper on the conical solar dials of 

 the ancients, particularly that of Ileracleus of Latmos, with 

 a view to bring to light the amount of knowledge possessed 

 by their constructors. The interior surface of these dials 

 constituted a cone, the section of which by the upper hori- 

 zontal surface was a curve of the second degree, either an 

 ellipse (as in the dial of Ileracleus and the Naples dial), a 

 hyperbola (dial at Athens), or a parabola (Phoenician dial). 

 The latter curve requires that one of the generatrices of the 

 cone should be rigorously horizontal, and has been only once 

 observed. But the dials were not made in this way : the 

 cone was traced with any convenient proportions, subject 

 only to the condition that its summit should be on a per- 

 pendicular from the centre of the base. 



Professor Mayer has called attention to a curious bit of 

 history in relation to Young's theory of colors. It appears 

 that Young first adopted red, yellow, and blue as the prima- 

 ry colors, and that subsequently, taking it for granted th.it 

 "Wollaston was correct when he asserted four natural divis- 

 ions of color in the solar spectrum, separated from each other 

 by dark lines, he adopted red, green, and violet, these being 



