OCTOBEE 2, 1896. J 



SCIENCE. 



489 



based on all available data, give a maximum 

 pressure of 125 pounds per square foot. The 

 direction of the whirl is stated to have been 

 from right to left. As this tornado occurred 

 in the southern hemisphere we should have 

 expected a movement from left to right. Per- 

 haps this whirl is described as if it were 

 looked at from the outside, and not, as we 

 are accustomed to describe our whirls, as if 

 we stood at the center and looked out at 

 the circulating winds. If the former is the 

 case, then the right to left in the published 

 account would mean left to right from our 

 point of view, and the Arroyo-Seco tornado 

 would follow the general rule. Or, it may 

 be that this tornado was one of the very 

 rare exceptions and really whirled in the 

 northern hemisphere fashion, instead of fol- 

 lowing the fashion of its own hemisphere. 

 A view of the damage done by this tor- 

 nado was published in Vol. X. of the Amer- 

 ican Meteorological Journal (opp. p. 350), 

 and is interesting from the fact that the 

 original view is probably the only photo- 

 graph of a southern hemisphere tornado 

 ever taken. 



ATMOSPHERIC DUST OBSERVATIONS. 



One of the many interesting branches of 

 the new meteorology is the study of the 

 number of dust particles in the atmosphere, 

 and of their effect in causing the condensa- 

 tion of water vapor in clouds, fog, rain or 

 snow. Aitken's papers in this connection, 

 published in the Proceedings of the Eoyal 

 Society of Edinburgh, have made this sub- 

 ject more or less familiar to all scientific men, 

 but comparatively little use has as yet been 

 made of his Dust Counter by others than 

 the inventor, although much important 

 work can undoubtedly be done along the 

 lines suggested and followed by him. In a 

 recent paper on Atmospheric Dust Observations 

 from Various Parts of the World (Quart. Journ. 

 Eoy. Met. Soc, July, 1896), Fridlander 

 gives many interesting results obtained by 



him with an Aitken Pocket Dust Counter 

 during a voyage around the world. Space 

 permits mention of only a few of the most 

 striking facts. The average number of 

 dust particles per cu. cm. of air over the 

 Pacific Ocean during eight days was 540, 

 while, when the vessel was about 35Q 

 miles from Auckland, the number rose to- 

 1229, and when about 15 miles from the 

 Great Barrier Island it was 1972. The 

 average dustiness of the Pacific was 613,. 

 and that of the North Island of New Zea- 

 land, together with the polluted area out- 

 side of it, 1336. 



The clearing effects produced by fog are 

 plainly seen in the following summary, based 

 on many tests made on the Atlantic, the 

 Pacific and the Mediterranean : 



No. of particles per cu. cm. Condition of air. 



2000 Foggy at intervals. 



3000 Thick fog. 



420 Half hour after clearing of fog.. 



3120 Thick fog. 



280 Clear region just beyond fog. 



1550 Eegion farther out of fog. 



The lowest figures obtained by the author, 

 210, were found on the Indian Ocean after 

 much rain, and on another occasion the 

 number of dust particles at 10.30 a. m. 

 was 331, while at 11 a. m., after a shower, 

 it was 280. The purifying effects of rain 

 are thus clearly seen. 



It is a cause for regret that there is not a 

 large number of investigators in the United 

 States working on this interesting subject 

 of atmospheric dust. So far as we know, 

 there are but two of Aitken's dust counters 

 in this country. 



RECENT KITE-FLYING AT BLUE HILL OBSER- 

 VATORY. 



The exploration of the free air by means 

 of self-recording instruments elevated by 

 kites has been greatly advanced during the 

 present summer through the work done at 

 Blue Hill Observatory, 640 feet above sea 

 level, near Boston. The kites used are the 



