OF ARTS AND SCIENCES. 



iLi 



Athens, as a rule, were not Greeks ; they were barbarians, such as 

 Phrygians, Carians, Thracians. And yet their children could not be 

 distinguished from those of the descendants of the Autochthones. 

 The obvious inference is, either that there was no great difference be- 

 tween the exterior of the Hellenes and that of the neighboring races, 

 or that many barbarians might be taken for Greeks, and many Greeks 

 for barbarians. 



Professor Bond exhibited a diagram of the outline of the 

 head of the great Comet of 1858, compared with a parabola 

 having its focus at the nucleus, and its axis coincident with 

 the initial axis of the tail, the curve touching the outline at 

 its apex. 



In this position the two curves should coincide, if we suppose the 

 paths of the particles forming the tail, after being emitted with equal 

 initial velocity in all directions from the nucleus, to be determined by 

 the repulsive force of the sun, alone, or in conjunction with a repulsion 

 from the nucleus, sensible only at a small distance from it.* 



The Plate represents a gi-oup of normal outlines of the head of the 

 Comet, with the position of the nucleus corresponding to each, deter- 

 mined from actual observations for the dates September 17 and 30, and 

 October 7 and 14, 1858. The second group shows the curve of a para- 

 bola having its focus at the nucleus, and enclosing the normal outline of 

 the Comet on October 4, with the curve of a catenary imposed upon it. 

 The approximation of the latter to the outline of the Comet is remarka- 

 ble. On the other hand, the divergence of the parabola is decided, 

 and shows the necessity of some modification of the above hypotheses. 



The existence of an atmosphere holding the particles in suspension 

 previously to their being driven off into the tail would tend to contract 

 its outline, and afford in this particular a nearer agreement with the ob- 

 served figure ; a similar effect would be produced if we suppose the 

 initial velocity of the particles, on leaving the vicinity of the nucleus, 

 to diminish when the angle between the direction of emission and that 

 of the sun increases ; or, again, if the direction of emission from the 

 nucleus is limited to a comparatively small range on either side of 

 the sun. 



* Bredichin, Astron. Nach. 1291, p. 292. Norton, Am. Jour, of Science, 

 XXVII. p. 87 ; XXIX. p. 384. 



