•June 10, 1921] 



SCIENCE 



535 



ond spot would replace the first in relation to 

 the earth. If the first spot gave rise to emis- 

 sion of ions, radially, which in its orbital mo- 

 tion the earth reached and in which it became 

 enveloped, the aurora of May 13 was possibly 

 the result. The same relation repeated a day 

 later by the second spot replacing the first 

 would account for the aurora of May 14. 



The relation of the two auroras in time, and 

 the sequence of spot positions on the revolving 

 sun are significant to say the least. 



In this connection it may be noted that the 

 great aurora of March 22, 1920, had a very 

 long and unusual duration, beginning early in 

 the evening of that day and continuing all 

 night, even being observed just before sun- 

 rise on the 23d. It may have continued 

 during part of that day, invisibly of course. 

 At that time an examination of the solar 

 surface disclosed a remarkably elongated spot 

 area or chain of spots, and at each end of the 

 chain or elongated group was a well-marked 

 rounded spot. The group was fairly uniform 

 in width extending in a direction nearly paral- 

 lel to the solar equator, and its length would 

 amply account for the long continuance of 

 the aurora if emanations were pouring out 

 from the whole group as it revolved with the 

 the sun. Moreover, its advance past the me- 

 ridian of the sun was apparently much the 

 same before the aurora as with the two spots 

 believed to have caused the auroras of this 

 year on May 13 and 14. Such an advance 

 points to a period (several hours possibly) 

 required for the ionic emanations from the 

 spot area to traverse the radius of the earth's 

 orbit, from the sun. 



Another matter of interest may be men- 

 tioned. In many auroras, especially during 

 the greater outbursts, there occurs at times 

 the peculiar streaming upward, as if a lumi- 

 nous wave was running up toward the zenith 

 crown; a sort of flaming effect. The motion 

 is fairly rapid, perhaps one half second being 

 required to traverse the length of the streamer. 

 The point I wish to make is that the apparent 

 velocity of this wave-like luminosity upward 

 seems to be constant in all auroras that I 



have witnessed and in which it was possible 

 to make an estimation. This should be con- 

 firmed or denied by measurement, for those 

 streamers which bear the same relation to the 

 observer, as variations in distance away may 

 affect the result. 



Elihu Thomson 

 SwAMPScoTT, Mass., 

 May 16, 1921 



THE LANDSLIDE NEAR MONT BLANC 



The March Bulletin of the Eoyal Italian 

 Geographical Society contains an account, 

 well illustrated with map and photographs, by 

 Professor TJ. Valbusa of the landslides near 

 Mt. Blanc which occurred on the 14th and 

 19th of November last and made much stir 

 in the newspapers, even to the point of ex- 

 citing fear that the roimd-topped " monarch 

 of mountains " had lost some of its height 

 (4,807 meters). Such was by no means the 

 case, as the head of the slide was on the east- 

 ern side of the subordinate dome known as 

 Mt. Blanc de Courmayeur (4,Y09 m.), two 

 kilometers east of and nearly 500 meters lower 

 than the main mountain dome. Granite rock 

 masses about half a square kilometer in total 

 slanting area, were dislodged from the over- 

 steepened side of an east-facing spur, the 

 top of the gray slide-scar being a little lower 

 than the terminal point of the spur which 

 has an altitude of 4,381 meters. The de- 

 tached rock masses first slid down into a 

 second-order cirque of small size between the 

 spur of origin and the Aiguille blanche de 

 Peteret, near by on the southeast; there they 

 turned a short distance northeastward and de- 

 scended from the hanging outlet of the small 

 cirque to a level of about 3,200 meters on the 

 Brenva glacier at the western side of the great 

 first-order cirque in which this glacier gathers 

 its neve branches, and from which a narrower 

 glacial tongue cascades southeastward into 

 the over-deepened trough — locally known as 

 the AUee blanche — of the uppermost Dora 

 Baltea. On reaching the main glacier be- 

 neath the small cirque, the slide turned to 

 the right, and gathering ice as it rushed along 

 spread over the whole 3-kilometer breadth of 



