494 



METEOROLOGY. 



E. Curtis has sought to determine what advan- 

 tages the spread vane possesses, as compared 

 with a straight vane of the same length and 

 shape, and at what angle the wings should be 

 set to secure the greatest efficiency. From cal- 

 culations based upon the results of experiment, 

 he deduces formula showing that the oscilla- 

 tions of both vanes are smaller as the vanes 

 are longer and larger; that the spread vane is 

 always more stable than the straight vane ; 

 and that this advantage in stability is greater 

 for long vanes than for short vanes, and is in- 

 dependent of the wind velocity. The analysis 

 obtains for a frictionless bearing. From the 

 discussion of relative sensitiveness, it is found 

 that, with equal friction, a spread vane is more 

 sensitive than a similar straight vane ; conse- 

 quently, for two vanes of equal sensitiveness, 

 the spread vane will have the greater friction, 

 and will come to rest more quickly. 



The name of Foehn is applied in Switzerland 

 to the occurrence hi mountain-regions, espe- 

 cially in winter-time, of a warm or even hot, 

 dry wind, blowing briskly down the valleys 

 from the high cold passes. The wind is com- 

 monly accompanied by a bank of dark clouds 

 over the pass at the head of the valley from 

 which it descends. The effects of the high 

 temperature and aridity are often very marked. 

 Similar phenomena have been observed in 

 New Zealand and in the Andes at San Jnan in 

 the Argentine Republic, where the wind is lo- 

 cally called the Zonda; and they are exempli- 

 fied in the Chinook winds of our western Cor- 

 dilleras. The Foehn was formerly supposed 

 to be an extension of the dry, hot sirocco which 

 blows into southern Europe from the Desert of 

 Sahara; bnt investigation, as summarized by 

 Mr. W. M. Davis, has shown that its phenom- 

 ena are incompatible with this view, and it is 

 now regarded as of local origin. It is, in fact, 

 a result of the changes of temperature which 

 the cyclonic winds undergo in their successive 

 ascent and descent as they cross the tops of 

 the mountains. In rising to the summit these 

 winds are cooled, and precipitate their vapor 

 in the form of rain or cloud. The air, now 

 dried, being compressed as it descends the 

 mountain, becomes warmed more rapidly than 

 it had been cooled in the ascent, and emerges 

 upon the plains below as a warm, drying wind. 



Electricity. Some remarkable phenomena of 

 fire-balls and globular lightning were described 

 at one of the meetings of the Royal Meteoro- 

 logical Society. Both were observed many 

 years ago, but have only now invited scientific 

 attention. Two ladies, walking on a cliff at 

 Ringhead Bay, Dorset, in the afternoon, saw 

 all around them, and from near the surface of 

 the ground to two or three feet over their 

 heads, numerous globes of light, the size of 

 billiard-balls, of various colors, moving inde- 

 pendently up and down, sometimes very near 

 them, but always eluding their grasp. They 

 varied in numbers from as few as twenty to 

 thousands. The display was without noise of 



any kind. Dr. J. "W. Tripe related that, during 

 a thunder-storm in 1874, he saw a ball of fire, 

 of a pale yellow color, rise from behind some 

 houses, at first slowly, then with increasing 

 speed, till its progress became so rapid as to 

 form a continuous line of light, proceeding 

 first east, then west, and rising all the time. 

 At last, after having described several zigzags, 

 it disappeared in a large black cloud to the 

 west, from which flashes of lightning had come. 

 In about three minutes another ball ascended, 

 and in about five minutes afterward a third, 

 both of which behaved like the first one, and 

 disappeared in the same cloud. 



The loss of electricity by a conductor in 

 moist air has been studied by Signer Gugliel- 

 mo. He finds that, with potentials less than 

 600 volts, moist air insulates as well as dry air, 

 but with higher potentials there is more loss 

 in moist air, and more the moister the air and 

 the higher the potentials. The potential at 

 which the difference becomes perceptible is 

 the same for a ball as for a fine point. It oc- 

 curs with extremely smooth surfaces, and so 

 can not be attributed to discharges in conse- 

 quence of roughness of surface. With equal po- 

 tential the loss of electricity has the same magni- 

 tude, whatever the dimensions of the balls used 

 as conductors. In air saturated with vapors of 

 insulating substances, the loss of elasticity of a 

 conductor is nearly the same as in dry air. 



The statistics of damage from lightning in 

 Schleswig-Holstein, Baden, and Hesse, show 

 that the danger from lightning in those parts 

 (unlike the experience of other parts of Ger- 

 many) has been decreasing of late years. 

 Thatched houses are fired about seven times 

 oftener than houses with hard roofs. Wind- 

 mills and church and clock towers are struck, 

 respectively, fifty-two times and thirty-nine 

 times oftener than ordinary houses with hard 

 roofs. The marshy regions in Schleswig-Hol- 

 stein are the most dangerous, and the land 

 about inlets of the sea-coast is the safest. 

 With like conditions, the relative danger de- 

 creases as the houses are more closely grouped 

 together. The geological nature of the ground, 

 especially its capacity for water, has important 

 influence. Calling the danger on limestone 

 one, that for sand is nine, while for loam it is 

 twenty-two. Four factors affect the danger to 

 buildings from lightning: two physical un- 

 equal frequency of storms, and geological char- 

 acter; and two social variable population and 

 mode of building. Of all trees, oaks are most 

 frequently damaged, and beeches most rarely, 

 the ratio between the two being as 54 to 1. 



As bearing on the extent to which the effect 

 of a lightning-flash may be felt, M. D. Calla- 

 don relates an observation of an electric dis- 

 charge at Schonen, in the Canton Bern, on the 

 7th of April, which, after striking a large pop- 

 lar, spread havoc for some hundreds of metres 

 around, with results comparable to those fol- 

 lowing the explosion of a large powder-maga- 

 zine. 



