Your letter containing the Spiral spring was recieved in due time. a mode of constructing your polygraph which might render it more portable occurred to me and as it took me less time to give verbal directions to my workmen for a model, than to make a drawing for you, I have had a model made which I send you by this post. it is of half size in all it’s dimensions, whence you will see that in full size it will not be larger than a very moderate portfolio. whether any or all it’s parts may be of any use, you will judge. I was not satisfied whether the admitting the North side to have a sideling motion, preserving it’s parallelism, & also a North & South motion, might not be found useful, & therefore the interior hole in the brace is made. it will require inkpots with effective stoppers for travelling, which are easily made.

If the publication of the 6. lines of my letter of Aug. 19. will be of service to you, certainly they are at your service. but as they were hastily & carelessly written be so good as to strike out ‘I only lament &c. to ‘possession,’ and insert instead of it ‘I only regret it had not been invented 30. years sooner, as it would have enabled me to preserve copies of my letters during the war, which to me would now have been a consoling possession.’ let me know whether the idea of the model answers and accept my friendly salutations.