KX I'EIUJIENTS WITH IONIZED Mil. 



dear water remains uniformly Hlimeiitary, so long as a certain critical velocity 

 of efflnx is not exceeded. After tliis the jet l)reaks up suddenly an<l violently into 

 eddies. Hut as applied to the steam jet, this ie;uson is not quite adequate ; for if 

 the intensity of the latter is still further increased, magnificent browns and oranges 

 ai)i)ear l)ey>iii(l the ()])aque. To account for opacity it is thus essential to inquire 

 into the lelation of color to size of particle at the point where color is extinguished. 



4. yV/c- bouudarief! of the opaque region. — The final sul)ject to which atten- 

 tion must here be directed is the relation of the color obtained from a given influx 

 of nearly pure air, its temperature, and the pressure actuating the steam jet. I 

 apj>end two illustrative charts, figures 7 and 8, from my earlier paper. In these 

 the ai>scissas indicate the temperature (in degrees centigrade) of the air entering 

 the color tul)e at C, figure 1, or in other words, the registry of the thermometer t, 

 figure 3. The ordinates show the pressure in centimeteis of mercury under which 

 the steam is forced out of the jet. Points of the curve between (t and 40 centi- 

 metei's then show the coiresponding values of air temperature and steam pressui'e 

 at which the dark violet of the first order merges into oparpie. The points of the 

 curve lying quite above 40 cm. (this datum (le[)eiids on many factors) show the 

 condition at whicli the l)iown j^ellows of the first order just emerge from opaque. 

 Curves indicating the ai)proximate loci are drawn through the points. 



Below 9°, therefore, the field is opaijue at all pressuies. Above \) , the pres- 

 sure at which the blue changes to opaque rapi<lly increases with increasing tem- 

 perature ; and the pressure at which brown yellow changes to opaque decreases 

 from an enormous value, and at even a moie lapid rate, as temperature inci'eases. 

 Both loci curving at a retaided rate, eventually reach a common asymptote at, say, 

 41 cm., the tempei'ature being indefinitely high. At the same time the colors 

 which wei'e very intense at the lower temperature gradually become fainter and 

 the opaque zone more tianslucent, until at about 40 of air temperature (de[)endinf' 

 on the size of the nozzle) the field is quite cleai' and without color. The escaping 

 steam is gaseous and not visibly condensed. When temperature decreases a^'ain 

 from 40% faint white yellow is tlie first color to appear, showing that the particles 

 here nuist be the smallest of the whole series. At 35° the change from faint 

 yellowish tones to faint white blues, when pressure is made to vaiy suitably from 

 largei- to smaller values, is quite mai'ked. There is no opaque demarcation, how- 

 evei-, but rather a mixture of colors, for the field is scarcely impervious to light 

 above 30°. 



For all temperatures and pressui-es lying to the left of the two cuives, fi<Tures 

 7 and 8, the field is ojxique, and it sends oil" a kind of cusp to penetrate into the 

 higher temperatures. There is a characteristic ditt'ei'ence between the two margins ; 

 for wliereas the yellow opacpie after a shai'p infiection shoots up almost vertically, 

 blue opaque shows a regular curvature throughout into lower temperatures than 

 the other. At al)out 1 ."i I have inscribed the successive position of the chief 

 colors. This caiuK^t l)e nearly so well done as the location of the opaque margin ; 

 but the contour of the color curves is surmised from the line for blue opaque. 

 Similarly above the yellow opaque line, a family of browns, oranges, and yellows 



