694 



STOEM-SIGNALS. 



before rain begins. It is the forerunner of the 

 lurid display of the thunder-storm, as Tennyson 

 has painted it : 



" The wild unrest that lives in woe 

 Would dote and pore on yonder cloud, 



That rises upward always higher, 

 And onward drags a laboring breast, 

 And topples round the dreary west, 



A looming bastion fringed with flre." 



The "pocky cloud" is an almost unerring 

 storm- warning. If clouds be red and lowering 

 in the morning, the red color arises from a 

 large amount of vapor in the vesicular state, 

 when, as Forbes has shown, the blue rays of 

 light are absorbed and the yellow and red rays 

 pass. This gives rise to the weather-proverb 



" The evening gray and the morning red 

 Put on your hat or you'll wet your head " 



and may sometimes prove ominous of a storm. 



The approach of the " Northers " of Texas 

 and Mexico is generally indicated, as an emi- 

 nent observer tells us, by "First, a general 

 humidity of the atmosphere. Secondly, the 

 peak of Orizaba Mountain visible and clear, 

 the lower parts only being enveloped in dense, 

 hazy clouds. Thirdly, the distant mountains, 

 far inland to the southeast, exceedingly clear, 

 together with excessive heat and depression in 

 the animal kingdom." 



Prof. Brocklesby has well pointed out the 

 additional and important fact that the top of 

 the storm always impends overhangs the 

 track on which it is advancing, because the 

 base of the storm is retarded by friction with 

 the earth's surface. This is of great signifi- 

 cance, as always enabling the close observer to 

 give warning. This is more easily done, from 

 the fact that the front of most storms is 

 marked by a moist, warm atmosphere. 



In the northern parts of the United States, 

 according to Prof. Espy, the wind in great 

 storms generally sets in from the north of east, 

 and terminates from the north of west ; while 

 in the southern parts it generally sets in from 

 the south of east, and terminates from the 

 south of west. 



Perturbations of the magnetic needle are in- 

 separably joined with one or more of the three 

 following phenomena: 1. General disturb- 

 ances of the telegraphic lines due to wide- 

 spread auroras, which mark general move- 

 ments of the atmosphere in high latitudes and 

 over the Atlantic. 2. Disturbing currents of 

 a more local character, occurring over the 

 telegraphic lines some time before the storm 

 appears to which they owe their origin, thus 

 lengthening the distance and time at which 

 the approach of the storm may be perceived. 

 3. Disturbing currents, still more restricted, 

 accompanying the electric changes when the 

 storm itself is passing. Blood-red streamers 

 of aurora crossing the sky and meteoric and 

 electrical exhibitions preceded the gale in 

 which the Eoyal Charter went down. If we 

 could have more magnetic and meteorological 

 observations, the magnetic and electric states 



of the atmosphere and auroras might be made 

 our most valuable prognostics of storms. 



It has also been discovered that the pres- 

 ence of large quantities of ozone (which can 

 easily be ascertained by ozone test-papers) 

 foreshadow an impending atmospheric storm. 



These unbidden monitions, together with 

 many others as the sun setting red, a remark- 

 ably red color of the clouds; the sign almost 

 infallible, at Mauritius, of the brick-dust haze 

 in the horizon; a thick, muddy atmosphere, 

 but extraordinarily clear on mountains; fre- 

 quent shiftings of breezes from all points, 

 thick fog flying fast to the south, a bright halo 

 round the moon, stars very brilliant and un- 

 usually twinkling at low altitudes, noises in 

 caverns and wells like a storm, moisture on 

 walls and pavements, sea-birds coming to land, 

 water-fowl flying about ; the swell of the ocean 

 rolling in, though the hurricane may be 600 

 miles distant; turtles floating in the calm, ap- 

 parently in a state of stupor ; the sea peculiarly 

 clear at great depths, tides irregular ; branches 

 of trees not bent forward as by a stream, but 

 constantly whirled about; water rising in wells 

 and ponds ; disturbances of currents on the 

 telegraphic wires are some of the oft-ob- 

 served presages of the "thing of evil." 



Within a few years, vast improvements have 

 been made in meteorologic instruments, and 

 the instruments in use by General Myer are of 

 the most approved construction and of ex- 

 quisite delicacy. 



The ordinary barometer is that of Mr. James 

 Green, of New York, the standard adopted by 

 the Smithsonian Institute, and the Army and 

 Navy of the United States. This barometer is 

 after the original design of Fortin, in which 

 the error of level is entirely got rid of. To 

 the scale is attached a vernier by means of 

 which the variation of the mercury in the 

 tube is detected even to the i^th of an inch. 

 It is an exceedingly rare thing for an accident 

 to happen to this barometer. 



The thermometers used are both erect and 

 horizontal. By the first, the height of the 

 column of mercury, and hence the tempera- 

 ture at any given moment, is read with exact- 

 ness. By the latter, the maximum and mini- 

 mum thermometers, are ascertained the high- 

 est and lowest range of the temperature in 

 any given number of hours. These instru- 

 ments are hung horizontally on hooks, and are 

 never handled, the index in the tubes being 

 steel and, when read, the index is set by means 

 of a magnet. 



The thermometers at the station of the Sig- 

 nal Service are fixed in the Louvre "boarded 

 "box for thermometers, so scientifically con- 

 structed that, as nearly as possible, the mer- 

 cury is protected from solar radiation on the 

 one hand, and on the other, the circulation of 

 the air is not impeded, since the sides of the 

 box are open somewhat as window-shutters, 

 to allow ventilation. 



The hygrometric conditions of .the atmos- 



