|Has your counter part made a reply to this letter from Gothard Wren?|
I now understand what you meant by the second half giving a clue as to the time period. Clearly written at the bottom of the page.
Your piece brought me cause to look up the history of rockets. Which is what Dr. Adahlgiso's secret is unless I miss read something. Here is some of what I have found.
Profiting from their Indian experience, the British, led by Sir William Congrieve (KON-greeve), began development of a series of barrage rockets ranging in weight from 300 to 18 pounds. Congrieve-design rockets were used against Napoleon. It is surprising that Napoleon seems to have made no use of rockets in the French Army but it must be remembered Napoleon was an artillery officer and may have simply been too hide-bound a traditionalist to favor new-fangled rockets over more familiar cannons. The scope of the British use of the Congrieve rocket can be ascertained from the the 1807 attack on Copenhagen. The Danes were subjected to a barrage of 25,000 rockets which burnt many houses and warehouses. An official rocket brigade was created in the British Army in 1818.
Froissart's idea was the forerunner of the modern bazooka. Joanes de Fontana of Italy designed a surface-running rocket-powered torpedo for setting enemy ships on fire. In 1650, a Polish artillery expert, Kazimierz Siemienowicz, published a series of drawings for a staged rocket.
During the early introduction of rockets to England, rockets were used primarily for war. Many battles were fought where rockets played important roles. Francis Scott Key coined the phrase the "rocket's red glare" after the British fired Congreve rockets against the United States in the War of 1812. Congreve had used a 16-foot guidestick to help stabilize his rocket. William Hale, another British inventor, invented the stickless rocket in 1846. The U.S. army used the Hale rocket more than 100 years ago in the war with Mexico. Rockets were also used to a limited extent in the Civil War.
From what I see your story fits into the history well for the most part. A stickless rocket in 1813 would be an amazing secret to keep.