The Birmingham age-herald., 1910-12-18
HOW Av|ATORS
 GUAGE HEIGHT One of the Tricks of the New
 Profession THE SEVERAL METHODS And All Are Fairly Accurate-Baro- scope Not Yet Accepted by
 AlI-sextant Is Also
THE SEVERAL METHOD.
yrom the Springfield Republican.

From the Springfield Republican.
 Many people who have been to avia-
 tion meets in various places and great
 many more who content themselves with
 reading of the exploits of the birdmen
 wonder how the judges find out how high
 in the air the various aeroplanes rise and l how the altitude can be given In feet Several methods are in use, all of them
 fairly accurate, but one, at least, rather l difficult for the lay mind because of the
 mathematics involved. The baroscope Is
 the simplest method of measuring heights
 attained by aeroplanes, but great many experts are not ready as yet to acknowl-
 edge its complete accuracy and reliabili- l ty. During the recent meet on the Squan- l tum meadows near Boston, Prof. Robert w. Wilson of Harvard, had charge of the
 altitude measurements. He and his as-
 sistants did not have time to investigate
 the system In vogue abroad, but devised
 one of their own that proved highly sat- isfactory and accurate. It is said that
 had it been desired the altitude attained
 by soaring aeroplane could have been
 announced every few minutes. Two sys- tems were used and the results were
 used to check each other.
 1 The first system consisted of two sta- tions at either end of a 5o0-foot base
 line running north and south, the center
 Of the line being about in the center of
 the aviation field, where the aeroplanes
 started. The north and south direction
 was taken in order that the line of sight | fro ocho ct ion tuIt ha fo
 sible from the sun at that time of day when the conditions are favorable for flight. With this base line was estab- lshed a vertical plane of reference, and
 the aeroplanes were observed when they
 passed through the plane.
 | At each end of the base line was sex | tant reading to 10 seconds. These sex tants were provided with extensions for | both horizon glass and index glass for convenience in finding the aeroplanes
 and making an approximate setting with I tho naked eye as the time of transit ap- preached, to facilitate accurate observa- | ton at the critical moment To show the carefulness with which the observations were made, Professor Wilson stated that | the point determined was, as nearly as
 possible the center of the aviator's body | or when this was not distinctly visible.
 the estimated center of the wings of the aeroplane.
 | Sextants were selected because angles | up to and beyond the zenith could be
 measured without change of position Of | the eye. The sextant stations were con l nected with each other and with the conl-
 mittee when a graphic table was used to determine the altitude at once. The
 other system consisted of two stations
 or nearly an east and west base line of
 6236 feet. One station was at Quincy, | 125 feet above the center of the aviation
 field. and the other was in Milton, r feet
 above the aviation field. From these
 stations the angle of elevation could be
 measured without an eye piece prism up | to an altitude of more than 15.000 at the
 center of the field. The instruments used at these stations were a special
 theodolite magnifying 30 times and read
 ing horizontal angles to 10 seconds and
 vertical angles to 20 seconds. and a min ing transit reading both horizontal and vertical angles at 20 seconds These sta | tions were connected with each other and with the central station at aviation 1 field by telephone line. Regarding the
 observations Professor Wilson says: 'It was thus possible to secure simul- taneous observations at the two stations | in both co-ordinates. That they were practically simultaneous Is clearly shown by the complete discussion of the results. By the combination of the observations
 we were able to compute not only the all titude of the aeroplane at intervals of about 45 seconds, in some cases 30 sec onds. but also to locate their correspond ing position as projects vertically on tho