Octobeb 6, 1916] 



SCIENCE 



497 



center of the dome of the firmament, whose 

 vault was composed of bands and changing 

 masses of streaming light, the quivering waves 

 of which were surging upward toward the disk 

 of blue at its apex. A brighter arch spanned 

 the northern horizon, and this also was under- 

 going constant transformation. 



It was not the light itself, marvellous as 

 were its mass, zones, banners and steamers, 

 that most thrilled the observers. Such a vast 

 display of light in constant movement had 

 never before been seen nor imagined by any 

 of us. The whole heavens shuddered and 

 staggered, shivered into a swirling chaos and 

 reformed again and again in new and still 

 more weird aggregates of shimmering light. 

 Light streamed and wavered, rippled, flickered 

 and pulsated. Now it was in broad waves 

 reaching to the zenith, and now in vibrating 

 bands. Here a broad cone shot up from the 

 northern horizon until its apex pierced the 

 very mid-heavens, and in the twinkling of an 

 eye it was gone. There, from the shifting 

 zones around the zenith, ripples of light passed 

 upward to the blue apical disk. To the nat- 

 uralist no more apt figure of this rippling 

 motion could be suggested than the waves of 

 light passing along the meridional bands of 

 phosphorescent Ctenophora. 



Again, a delicate fringe of pencil points 

 would appear on the upper edge of one or 

 more of the shifting zones and then shoot 

 upward with inconceivable rapidity in sharp 

 vibrating pencillings of light. As mentioned 

 before, the focus of all these movements was 

 the zenith itself, which seemed to be under- 

 going an intense bombardment of waves, 

 ripples and searchlights from all sides, al- 

 though subsidiary lateral movements were 

 also in evidence. 



Marvellous as was the rapidity of move- 

 ment, the rapidity of change or kaleidoscopic 

 effect was no less astonishing. Over and over 

 again one of the observers would try to call 

 attention to some particularly vivid display, 

 only to find it utterly gone before the others 

 could turn their eyes in the direction indi- 

 cated. These changes were much more rapid 

 than in other auroras seen by the writer. 



Nothing but electrical phenomena could ap- 

 proach their instantaneous shiftings. 



At first the light was all pure white radi- 

 ance, exactly that of electricity. Later certain 

 areas took on a rose color, and still later the 

 display more closely resembled that of ordi- 

 nary auroras, being concentrated in the broad 

 arch across the northern sky and showing 

 more variety in colors. 



So absorbed were the observers in this grand 

 spectacle of light in motion that it was long 

 before they noted the peculiar effect of the 

 light upon themselves and their immediate sur- 

 roundings. Then we saw that it was a per- 

 fectly diffused light, coming in practically 

 equal intensity from all points of the sky. A 

 more unreal scene could hardly be imagined. 

 It was unlike moonlight, for there were no 

 shadows nor shadings. On that account all 

 objects seemed much less brilliantly illumi- 

 nated than they really were. It was most like 

 the light of early dawn ; but still different, for 

 in the dawn the light, although diffused, is all 

 from one side. Objects were distinctly visible, 

 but flat. Our companions' faces could be 

 seen quite plainly, but lacked individuality. 

 The opposite shore of the lake could be seen 

 much more distinctly than in bright moon- 

 light and objects inside the house were quite 

 distinct, even if small. 



How long the display lasted we do not know, 

 although one of the party reported it as stri- 

 king as ever well past midnight. Finally the 

 chill of the night and the aching of our 

 strained necks drove us indoors with the con- 

 viction that never again should we see such a 

 stupendous spectacle of light in motion. 



C. C. Nutting 

 State University of Iowa 



increasing depth of focus with the 



SWING-BACK 



To the Editor of Science: The writer ad- 

 mits his membership in the not inconsiderable 

 class of field workers who are never satisfied 

 with their photographic results. A little dis- 

 covery, however, recently enabled him to im- 

 prove the focus on certain classes of deep- 

 focus pictures and he excuses the description 



