STORM-SIGNALS. 



093 



phono at every station of the Signal Service 

 urv noted by means of the wot and dry hull) 

 th. nil-nil. -tt-rs, wlii.-h furnirdi the most relia- 

 ble indications of the moisture and saturation 

 of the air, and for ascertaining the dew-point, 

 relative humidity, and absolute humidity, and 

 <>thT aqueous phenomena. The readings of 

 this instrument are confirmed by those of an- 

 other instrument, the hygrodeik, which fur- 

 nishes all tho liygrometric results without any 

 calculations by the observer, who merely 

 copies certain figures to which the pointer of 

 the hygrodeik points. 



Invaluable as are the records made by ob- 

 servers from these instruments, their worth 

 has been almost eclipsed by the more re- 

 cent inventions of self-registering barometers, 

 thermometers, ete. Among this class of scien- 

 tific contrivances, General Myer has adopted 

 the " Self-Registering Anemometer " for show- 

 ing the velocity and force of the wind ; the 

 "Self-Recording Rain-Gauge ; " the Thermo- 

 graph of the Kew Observatory, indicating the 

 temperatures ; the Kew Barograph ; the Pee- 

 lor " Self-Recording Barometer; " Wild's Ber- 

 lin "Self-Registering Barometer;" and Prof. 

 Hough's celebrated Meteorograph and Self-Re- 

 cording and Printing Barometer. 



The meteorograph is an automatic machine 

 which writes its own indications in lead pencil 

 for every second in the twenty-four hours, upon 

 a roll of paper, which is divided by lines and 

 moves off a reel at a uniform rate of speed, 

 which is adjusted by a clock. It indicates 

 simultaneously the exact height, in inches and 

 hundredths of an inch, of the barometer, and 

 the wet and dry bulb thermometers. It thus 

 records at one and the same moment the press- 

 ure, the temperature, and the hygrometry, of 

 the air, with unerring precision. By a simple 

 application of the photographic art, the regis- 

 ter is taken on suitably-prepared paper, at the 

 instant the atmospheric changes are taking 

 place. This gives the Signal-Office an unim- 

 peachable account of the minutest ripple on 

 the great atmospheric ocean, and, when these 

 photographs are put into a volume, they fur- 

 nish a pictorial history of all the mutations of 

 weather within a known area of the earth's 

 surface. 



As far as the barometric annals are con- 

 cerned, the refinements of science have gone 

 even further than this degree of accuracy, 

 Hough's Printing Barometer not only doing 

 the same work of his meteorograph, but also, 

 by an automatic process, setting the type and 

 making an actual impression on the paper, of 

 its exact readings, once in every fifteen min- 

 ntes. 



The anemometer in use is that of Robinson, 

 consisting of four hollow hemispheres or cups 

 screwed on to the ends of two horizontal rods 

 of iron crossing each other at right angles and 

 supported on a vertical axis which turns freely. 

 When placed in the wind, the cnps revolve; 

 and the arms are of such a length that when 



a mil.- of wind has passed the anemometer, 

 600 revolutions are registered by the instru- 

 ment. The accuracy of its construction may 

 bo tested by conveying it rapidly through the 

 air on a perfectly calm day the distance of a 

 mile and back again the same distance, and 

 noting the number of revolutions made. The 

 number of revolutions is registered by a sys- 

 tem of index-wheels set in motion by an end- 

 less screw on the upright axis, which are read 

 off in tho same way as a gas-meter. The num- 

 ber of miles travelled by the wind during a 

 day, an hour, or any other specified time, is 

 found by multiplying the revolutions made in 

 that time by 2, and dividing by 1,000. The 

 rate per hour at which tho wind blows at any 

 time is found by observing the revolutions 

 made, say, in two minutes ; multiply by 30 and 

 2, or at once by 60, and divide by 1,000. Thus, 

 suppose 800 revolutions were made in two 

 minutes, the velocity of the wind would be at 

 the rate of 48 miles an hour. 



The observers at the various stations of the 

 Signal Service are all sergeants of the United 

 States Army. Previous to their entrance on 

 duty, they are required to pass successfully 

 through two examinations, after an extended 

 course of studies and special training at Fort 

 Whipple, Virginia. In this course they be- 

 come thoroughly conversant with the meteor- 

 ological treatises of Loomis, Buchan, and other 

 writers. They are also required to become 

 experts in practical telegraphy, so that they 

 can use the telegraphic instrument with ease 

 and accuracy. 



The first examination of applicants for the 

 post of observer-sergeant is but preliminary, 

 and, to be successful, the applicant must show 

 himself a good arithmetician, a writer of good 

 English, and well acquainted with geography, 

 especially the geography of the United States. 



In the final examination, which, like the 

 first, is conducted by an army board (consist- 

 ing of Colonel Garrick Mallery, Major L. B. 

 Norton, and Captain H. W. Howgate), the ap- 

 plicant is required to work out a variety of 

 practical problems in instrumental meteorol- 

 ogy, to display a full acquaintance with the in- 

 struments, and also with the laws of storms 

 and the general principles of his science. 



The observers, while under training at Fort 

 Whipple, are instructed in all the duties and 

 drills of the Signal Corps of the army, and 

 thus, in time of war, are ready for field duty. 



The arrangements by which observations 

 are taken at the different stations, and trans- 

 mitted thence by telegraph to the central office 

 at Washington, have worked with great har- 

 mony and accuracy of result. 



Every, observer takes his observations at the 

 same moment by Washington time and by in- 

 struments which have been carefully adjusted 

 to a standard kept at the central office. 



After taking his observations (thrice daily), 

 the observer writes them out in full (not in 

 figures) on manifold paper, which gives him at 



