The analytical inquiry into the death and subsequent recovery of Marie Roget has many Ampersandian aspects to it. Let's start with an excerpt from the story, a translated passage from the presumably fictional French newspaper L'Etoile.
Thus we see if the body found in the river was that of Marie Roget, it could only have been in the water two and a half days, or three at the outside. All experience has shown that drowned bodies, or bodies thrown into the water immediately after death by violence, require from six to ten days for sufficient decomposition to take place and to bring them to the top of the water. Even where a cannon is fired over a corpse, and it rises before at least five or six days' immersion, it sinks again, if let alone.
Oh, so many questions and thoughts my brain resembles a bumper car rink. Body thrown in immediately after death by violence? Does that mean one entering the water immediately after death by natural circumstances behaves different? Cannon fired over a corpse...does that mean the firing of the cannon (percussive forces) is purported to make a body rise or is the cannonball cutting through the water over a corpse or is the cannonball landing on a corpse? Exactly how common was cannon firings in 1840s? (See this posting on U.S. History timeline if your curious. https://americasbesthistory.com/abhtimeline1840.html )
Dupin, our hero, focuses on the statement made with absolute conviction that a body requires six to ten days to rise to the surface and the corresponding conclusion that it could not have been Marie Roget as she had only been missing for three days. In his rebuttle to the friend and sidekick we are calling Eap, Dupin states that the human body is not much heavier or lighter than the water in the Paris river. He at length discusses the concept of Specific Gravity, and so shall we.
To understand Specific Gravity, you have to begin with density. Density is simply how much stuff is packed into a space. Everything we can see has a density. Chairs. Bricks. People. Cars. Same goes for gases like air, hydrogen, helium and the rest. The "space" can be something simple, like a cylinder or a cube, or can be irregular, like the human body. Density explains why a clay brick is heavier than a brick the same size made from wood or from styrofoam. In these cases, the "space" is the same, but the amount of "stuff" crammed into that space is very different.
Let's focus on liquids and solids. Specific Gravity simply compares the density of something (baseball, dinner plate, pumpkin, etc.) to the density of water. The density of "something" is divided by the density of water to get a number we call Specific Gravity. When Specific Gravity is less than one, the "something" has a density that is less than water. When Specific Gravity is greater than 1, the "something" has a density more than that of water. Here are the Specific Gravities for some common "somethings":
- Apple 0.64
- Petroleum oil 0.88
- Blood 1.06
- Brick 1.92
- Concrete 2.37
Important to the point L'Etoile was making, things with Specific Gravity less than 1 will float.
My curiosity being piqued by this story, I did some online digging. I did not have access to several medical and scientific articles which wanted $10-$25 to read something that may or may not have answered my questions. I was left with, and grateful for, the public domain information.
First question: What is the Specific Gravity of the human body? An interesting paper was published in the 1920s by Frank Sandon, M.A. titled "A Note of the Specific Gravity of a Living Human Being." His results found that the Specific Gravity of males ranges from 0.92-1.0 and females ranges from 0.94 to 0.98. Conclusion drawn included that all girls and women can float. Boys under 13 and men over 50 can float. Some men between 13 and 50 will sink. Other references found were consistent in this range. The Specific Gravity of an individual person seems to reflect overall size, bone size, and amount of body fat.
Second question: Does Specific Gravity change for a dead body? Google provides access to all 400 pages of the 8th Edition of A Manual of Medical Jurisprudence, which was published in 1866, only four decades after Poe's own story. It report the Specific Gravity of a dead body can range from 1.08 to 1.1 but noted it would take little to make the body buoyant and that, no, not all dead bodies sink. A 1977 abstract from the Journal of Forensic Science on the buoyancy of bodies found 69% of their subjects floated in sea water, while only 7% floated in fresh water. The Specific Gravity of sea water is 1.025, which means most of the bodies tested in 1977 had Specific Gravities between 1.0 and 1.025.
Third question: the image at the top of this post is visually stunning, but could it really happen? Assume we are looking at a body floating a few feet below the surface and not one merely passing through that point on the way to the bottom. Neglect that one knee is up, while the hair is down and the other leg is straight with the foot gracefully pointed. The answer is: possible but not probable. For the body to stay "hovering" below the surface as shown, the forces pushing her down have to be equal to those pushing her back up. Any change in forces would tip balance to either sinking or floating. After all, lakes and rivers are not the tranquil, isolated systems they are in a laboratory.
U.S. History in the 1840s: https://americasbesthistory.com/abhtimeline1840.html
Specific Gravity of blood: https://en.wikipedia.org/wiki/Specific_gravity
Specific Gravity of common materials: http://www.csgnetwork.com/specificgravmattable.html