2 76 POPULAR SCIENCE MONTHLY. 



at moderate heights positively charged. This agrees with the results of 

 recent observations made from balloons up to heights of 3,000 meters. 



Since condensation will depend on the number of ions available 

 for nuclei, we have at once an explanation of the curious fact that 

 cloud-formation in the upper atmosphere is more copious in years of 

 frequent aurorse than when they occur rarely. In this connection 

 another odd coincidence may be mentioned. When sunspots are 

 numerous, Jupiter shines with a white light; when they are few, his 

 light has a reddish tinge. Now it is agreed that Jupiter is still at a 

 high temperature. If, therefore, sunspots cause aurorse on Jupiter, 

 and consequent cloud-formation, we must see less of the heated in- 

 terior in sunspot years than we do when his cloud-layers are not so 

 opaque. 



In 1899 von Bezold showed that the daily variation of the compass 

 over the earth's surface could be simply represented as follows. 

 Imagine two points, one in latitude 40° N., and one 40° S., to move 

 round with the sun. Then it is as if the north end of the compass 

 needle were attracted towards the northerly point, and the south end 

 toAvards the southerly. Eemembering that the air immediately above 

 the earth has a positive charge, we see that this effect would follow by 

 Ampere's rule, if the sun's heat caused two air-whirls, one in the 

 northern and one in the southern hemisphere, over the places of highest 

 temperature, the former rotating counter-clockwise, the latter clock- 

 wise. Such whirls would result from the sucking in of currents from 

 the slower-moving north latitudes and the faster-moving south lati- 

 tudes towards the mean latitude of 40°, in the northern hemisphere, 

 and similarly for the southern. If this be the true explanation, then 

 for a given frequency of sunspots, the amplitude of the diurnal varia- 

 tion should increase by the same fraction of itself for all parts of the 

 earth. Thus if A° is the amplitude at a given place in a year of no 

 sunspots, and A its value in a year for which Wolf's number express- 

 ing the relative frequency of spots is f, we ought to find A = 

 A° (1-f-af). Now the value of the coefficient a comes out .0064 from 

 whatever part of the world the observations be taken from which it is 

 calculated. 



Meteorites and Nehulce. 



To the man of science this discussion of terrestrial details will prob- 

 ably be the most convincing part of the evidence adduced by Arrhenius 

 for his theory. But it is time to turn from it, and follow, with lagging 

 imagination, the destinies of those particles, by far the greatest num- 

 ber, which miss the earth and the planets, and launch forth into 

 interstellar space. 



Many of them will meet similar streams ejected from other suns. 



