Seven Miles?
On 5 September 1862 James Glaisher and his aeronaut, Mr. Coxwell, took a balloon up from Wolverhampton until Glaisher blacked out. In Travels in the Air (1871 edition), the book the Public Domain Review features, he concludes they reached "fully seven miles", 36,000 to 37,000 feet. He gives three reasons, and each can be redone from the numbers he printed.
What he wrote down
"At 1h. 51m. the barometer read 10·8in. … I then looked at the barometer, and found its reading to be 9¾in., still decreasing fast, implying a height exceeding 29,000 feet. … My last observation was made at 1h. 54m. above 29,000 feet." … "I resumed my observations at 2h. 7m., recording the barometer reading at 11·53 inches, and temperature minus 2°."
He left the ground at 59°F and read minus 5° at 1:52. A barometer reading becomes a height through the air's temperature below it. Using his own temperatures, 9¾ inches does come out at about 29,000 feet above the ground, so his last firm number holds up. Above that, he was unconscious for seven minutes, and the three arguments begin.
The three arguments
1. The rates. "At this time (1h. 54m.) we were ascending at the rate of 1,000 feet per minute; and when I resumed observations we were descending at the rate of 2,000 feet per minute. These two positions must be connected…" Thirteen minutes, and the 11·53-inch reading at the end, fix how much height has to be gained and lost. If the balloon kept climbing at full speed and then flipped instantly to falling at full speed, it peaked at about 36,000 feet, Glaisher's figure. If it slowed and turned over a few minutes, the peak comes down. With the slowest turn the readings allow, it is about 32,000. Move the second slider.
2. The thermometer. "A very delicate minimum thermometer read minus 11°·9, and this would give a height of 37,000 feet." On this ascent the air cooled 64°F between the ground and 29,000 feet. Carrying on at that rate, minus 11.9° is reached at about 32,000 feet. To get 37,000, the air above 29,000 feet would have had to cool at well under half the rate of the air below.
3. Coxwell's glance. Coming down from the ring, Coxwell "noticed that the centre of the aneroid barometer, its blue hand, and a rope attached to the car, were all in the same straight line, and this gave a reading of 7 inches". Seven inches does give about 37,000 feet. This is the only one of the three that supports the high figure without generous assumptions. It is a sighting along a rope by a man whose hands had just frozen, made after the fact.
So the evidence supports something above 32,000 feet. Seven miles needs the instant turn and Coxwell's glance.
Smaller things in the PDR's piece
| PDR | The book | |
|---|---|---|
| Tissandier at Calais "in August 1869" | "It was the 12th of August, 1868, I was at Calais"; the illustration list says "August 17, 1868" | year off by one |
| a poster "advertising a balloon launch from the central square the next day" | an ascent "fixed to take place on Sunday, the 16th", four days later | not the next day |
| "off the Neptune rises, 4,000 feet in a single bound" | "In one bound the Neptune rises to the crest of the clouds … we are already near 4,000 feet high" | matches |
| "At 5,200 feet, the pilot notices that the cumulus clouds 2,000 feet below them" head back to Calais | "we, at a height of 5,249 feet" … "those cumuli which we passed through at the height of 1,969 feet": the clouds were at 1,969 feet, about 3,300 feet below. Both figures are round metres converted (1,600 m and 600 m). | the 2,000 is the clouds' height, not the gap |
| life vests "purchased from the Calais Humane Society" | "I ran to the Humane Society's office to get some life-belts and floaters" | matches |
| preface "penned but a month after the lifting of the siege in March 1871" | signed "March 1871" | matches |
| "Sixty-seven manned flights" left besieged Paris | Godard's table in this edition numbers 62 balloons, the last "Le Cambronne" on 28 January 1871; its footnote says "The total number of balloons sent out by the Post Office during the siege was 54." Wikipedia says around 66. | the book itself says 62 (or 54) |
What stands on what
| Item | Source |
|---|---|
| All quotations and readings | J. Glaisher (ed.), Travels in the Air, 2nd ed. (1871), Internet Archive item travelsinair00flam: OCR text, checked on the page images of pp. 53, 54 and 57 and the balloon table |
| Heights from pressures | My arithmetic: the hypsometric equation with a straight-line temperature profile between the ground (59°F) and the reading's own temperature. Glaisher's own reductions may have used other corrections. |
| The rate model | Mine: climb at 1,000 ft/min, a steady change of speed lasting the chosen time, then fall at 2,000 ft/min, constrained to end at the 2:07 reading |
| About 66 siege balloons | Wikipedia, Siege of Paris (1870–1871) |