pilot balloon ascension chart
Date1909
Inventory Number1998-1-1051f
ClassificationMeteorological Chart
Subject
Maker
Blue Hill Meteorological Observatory
1885-present
Cultural Region
Place of Origin
Dimensions56.2 x 81.2 cm (22 1/8 x 31 15/16 in.)
Material
DescriptionGraphs of altitude and direction of a pilot balloon ascent from Blue Hill Observatory on October 7, 1909. Graph in upper left tracks the altitude by minute; graph in lower right tracks the direction by mile. Graph paper is made of large vertical rectangles bounded by thick lines, containing 25 smaller rectangles bounded by semi-thick lines, which in turn contain four rectangles bounded by thin lines.
The vertical axis of the altitude graph ascends from sea level to 6300 meters in intervals of 900 at every three semi-thick lines. On the other side of the axis, the altitude is marked in miles. The horizontal axis, located above the graph, ascends from 0 to 50 in numbered intervals of 5, each minute demarcated by one of the fine lines. The line on the graph begins four fine-line spaces from the right at a circled point. The altitude at each minute is marked by an x. The minutes are written at each point, with 11, 21, 31, and 50 written in larger font.
The horizontal axis of the direction graph ascends from 0 to 9600 meters and 0 to 7 miles. Above and to the right of this graph is a compass with east pointing upward. The line on the graph begins at the same origin, tracks to the "north" briefly, and then begins to curve around to head in a southerly direction until it begins to drift southwest. The minutes are written at each point, with 11, 21, 31, and 50 in the larger font.
The vertical axis of the altitude graph ascends from sea level to 6300 meters in intervals of 900 at every three semi-thick lines. On the other side of the axis, the altitude is marked in miles. The horizontal axis, located above the graph, ascends from 0 to 50 in numbered intervals of 5, each minute demarcated by one of the fine lines. The line on the graph begins four fine-line spaces from the right at a circled point. The altitude at each minute is marked by an x. The minutes are written at each point, with 11, 21, 31, and 50 written in larger font.
The horizontal axis of the direction graph ascends from 0 to 9600 meters and 0 to 7 miles. Above and to the right of this graph is a compass with east pointing upward. The line on the graph begins at the same origin, tracks to the "north" briefly, and then begins to curve around to head in a southerly direction until it begins to drift southwest. The minutes are written at each point, with 11, 21, 31, and 50 in the larger font.
Signedon chart: PILOT BALLOON ASCENT / FROM / BLUE HILL OBSERVATORY / OCTOBER 7, 1909
Inscribedupper graph, middle: ALTITUDE
upper graph, vertical axis, left side: METRES / 6300 / 5400 / 4500 / ... / 900 / SEA LEVEL
upper graph, vertical axis, right side: 4 MILES / 3 MILES / 2 MILES / 1 MILE
upper graph, horizontal axis (top): 0 5 10 ... 50
lower graph, upper middle: DIRECTION
lower graph, horizontal axis (bottom), upper line: 1 / MILE 2 / MILES 3 / MILES / ... / 7 MILES
lower graph, horizontal axis (bottom), lower line: 0 2400 4800 7200 9600 METRES
FunctionPilot balloons were used to measure velocity and direction of wind currents in higher layers of the atmosphere. They did not carry instruments and were therefore cheaper than larger ballon-sondes and could be used more frequently. The balloon would be tracked with one or two theodolites. The one-theodolite method used an assumed velocity of ascent, while the two-theodolite method would allow the altitude to be determined through triangulation. The one-theodolite method was sometimes advantageous, because it could be set up more quickly when conditions became favorable, and it actually proved superior in some cases where the balloon was too distant to triangulate accurately.
The lift is given for each balloon flight, as it was dependent on the amount of hydrogen put in it, and therefore roughly constant if leakage and tension in the rubber of the balloon was assumed to be zero. The velocity function could be given as a function of the lift and the density of the air. As the balloon ascended, the ratio of the density of the hydrogen in the balloon and the density of the surrounding air would be fairly constant, as the balloon's radius would increase with the decrease in air pressure during the ascent. The velocity of the balloon would vary inversely with the density of the air, so the balloon would increase in vertical velocity as it ascended. This allowed meteorologists to use a velocity function to calculate height when using the one-theodolite method.
Given the variation in the change in altitude of the balloon, it is most likely that the two-theodolite method was used to measure the height. Unlike the others in this group, this chart shows both the change in altitude and the change in direction of the balloon, which could then be used to determine the wind direction at different heights in the atmosphere. It might also be used to determine wind velocity along a horizontal trajectory, but as there is no vertical axis, only one component of the velocity vector could be calculated.
The lift is given for each balloon flight, as it was dependent on the amount of hydrogen put in it, and therefore roughly constant if leakage and tension in the rubber of the balloon was assumed to be zero. The velocity function could be given as a function of the lift and the density of the air. As the balloon ascended, the ratio of the density of the hydrogen in the balloon and the density of the surrounding air would be fairly constant, as the balloon's radius would increase with the decrease in air pressure during the ascent. The velocity of the balloon would vary inversely with the density of the air, so the balloon would increase in vertical velocity as it ascended. This allowed meteorologists to use a velocity function to calculate height when using the one-theodolite method.
Given the variation in the change in altitude of the balloon, it is most likely that the two-theodolite method was used to measure the height. Unlike the others in this group, this chart shows both the change in altitude and the change in direction of the balloon, which could then be used to determine the wind direction at different heights in the atmosphere. It might also be used to determine wind velocity along a horizontal trajectory, but as there is no vertical axis, only one component of the velocity vector could be calculated.
ProvenanceFrom the Blue Hill Meteorological Observatory.
Blue Hill Meteorological Observatory
Date: 1900-1920
Object number: 1998-1-1051e
Blue Hill Meteorological Observatory
Date: 1909
Object number: 1998-1-1051c
Boston and Albany Railroad
Date: early-twentieth century
Object number: 1998-1-0984g
Friez Instrument Division, Bendix Aviation Corporation
Date: circa 1956
Accessories: one used Taylor Instrument Companies paper chart and cardboard box; recording charts, Air Ministry, Meteorological Office, Form 4213, Barogram (18); one used "Self Recording Thermometer" chart. Richard Brothers Manu. PS Paris. "Blue-hill Meteorological Observatory"; one set of "Instructions for the Installation of Charts", Bendix Aviation Corporation, Friez Instrument Division, Baltimore 4, Maryland; Friez I.B. No. 165/Friez Part No. 509673-B
Object number: 1996-1-0190b
Blue Hill Meteorological Observatory
Date: 1911
Object number: 1998-1-1051d
Blue Hill Meteorological Observatory
Date: 1934
Object number: 1998-1-1434
Gerber Scientific Inc.
Date: circa 1950
Accessories: instruction booklet (with instrument); light brown leatherette case with brown velvet lining; six sheets of graph paper
Object number: 2003-1-0234
Walter Balcke
Date: 1955
Accessories: mahogany box with plexiglass lid; pencil; eraser; box of lead; putty ball; cleaning cloth; cardboard instruction card
Object number: 1997-1-1619
