During Thompson's apprenticeship those questions were agitating the public mind which finally had their outcome in the War of Independence. Mr. Appleton was one of those who signed the agreement refusing to import British goods, and this so affected the trade of the store that he had no further need for the apprentice. Hence it was that, in the autumn of 1769, Thompson went to Boston as apprentice-clerk in a dry goods store, but had to leave after a few months, through the depression in trade consequent on the non-importation agreement. His note-book, containing the entries made at this time, comprised several comic sketches very well drawn, and a quantity of business memoranda which show that he was very systematic in keeping his accounts. His chief method of earning money, or rather of making up the "Cr." side of his accounts, was by cutting and cording wood. A series of entries made in July and August, 1771, show the expense he incurred in constructing an electrical machine. It is not easy to determine, from the list of items purchased, the character of the machine he constructed; but it is interesting to note that the price in America at that time of nitric acid was _2s. 6d._ per ounce; of lacquer, _40s._ per pint; of shellac, _5s._ per ounce; brass wire, _40s._ per pound; and iron wire, _1s. 3d._ per yard. The nature of the problems which occupied his thoughts during the last year or two of his business life are apparent in the following letters:-- Woburn, August 16, 1769. Mr. Loammi Baldwin, SIR, Please to inform me in what manner fire operates upon clay to change the colour from the natural colour to red, and from red to black, etc.; and how it operates upon silver to change it to blue. I am your most humble and obedient servant, BENJAMIN THOMPSON God save the king. Woburn, August, 1769. Mr. Loammi Baldwin, SIR, Please to give the nature, essence, beginning of existence, and rise of the wind in general, with the whole theory thereof, so as to be able to answer all questions relative thereto. Yours, BENJAMIN THOMPSON. This was an extensive request, and the reply was probably not altogether satisfactory to the inquirer. On the back of the above letter was written:-- Woburn, August 15, 1769. SIR, There was but few beings (for inhabitants of this world) created before the airy element was; so it has not been transmitted down to us how the Great Creator formed the matter thereof. So I shall leave it till I am asked only the Natural Cause, and why it blows so many ways in so short a time as it does.