I have managed to get a copy of your book and I found it very interesting, and well worth the cost. I was very interested to see the amount of detail, not only with reference to other Langtons, but also notes of historic and political interest, farming and business as well as the weather.
It seems he avoided the south sea bubble with his investment in the canal instead. Seems he gained alot more shares in it around the time the bubble burst, which suggests he did well out of it because people who lost money would be desperate to sell their shares to him i would have thought.
From what i gather from other sources you have identified at least one additional diary of George's. I would be very interested in buying and reading another book based on additional diares if you decide to put one together. I would be especially interested to know George found the great frost of 1708/9. I understand the sea froze. Lakes and rivers froze, and the soil froze to a depth of a metre or more. Livestock died from cold in their barns, chicken's combs froze and fell off, trees exploded and travellers froze to death on the roads. It was the coldest winter in 500 years apparently. So how did George deal with it? Would be very interesting to know.