40 



TUE STKDCTUKE OF THE NDCLEUS. 



RESULTS I'OIJ AXIAL COLORS. 



19. Apparatus, co}iiad dr mm. — It will next be uecessaiy to devise ;ipp;initus 

 to show greater inteusity of axial color (tiie colors of the steam jet or color tube of 

 my first volume), with the necessary relation to the coronas. This was oiigiually 

 attempted with tubular apparatus ; but, in the interest of homogeneity, wide conical 

 apparatus was finally constructed, either a single or a double conical drum sub- 

 serving the puipose. Effective convection is then continually in action within, and 

 the density of distribution of cloml particles is uniform, slow work presupposed. 

 With the double drum (apices outward), not only can greater length of column be 

 secured, but small end windows of glass suffice. The instrument is thus less 

 troublesome than the single drum, the broad glass base of which is liable to break 

 exi)losively, after many exhaustions, from fatigued elasticity. 



The single drum is shown in figure 0, Ijeing made of sheet cop[)er, about 77 

 cm. long, 5 cm. in diameter at the smaller glass window, a, 30 cm. in diameter at 

 the larire slass window, bh. W is the Welsbach burnei' behind a small ciicular 



Vie. 6. — Conical Drcm. Ri;CErTAci.E for Condensation. Fig. 7. — Double 

 Conical Drum. Keceptaci.k eor Condensation. Fig. 8. — Diagram Relating to 

 Diffraction and to A.xial Colors. 



screen,'/, is the exhaustion and c the inflii.x tubulure holding a cotton filter,/". The 

 supply of water, w, keeps the air within saturated. The intei'ior walls must be 

 dull Idack to oliviate reflection from the sides of the drum as much as possible; 

 for all coronas are advantageously [trojected against a dark ground. Ribs /•, r, r, /; 

 prevent collapse under external pressure wlieu the interior is exhausted. 



When flame or axial colors are to be specially studied, it is best to remove the 

 screen from the burnei- and look at the fidl extent of the flame. Ground glass as 

 large as the window, a, ami illuminated l»y sunlight, is also very good. With the 

 eye at E, (tfi marks the i>ath of an axial color, (^yft the path of a diffraction color. 



The double drum, Ogiire 7, differs from the single drum merely l)y offering 

 a greater length of column for observation. It is 180 cm. long, 30 cm. in its 

 largest dianietei', and is carefully blackened within. The small windows, a, h, 



