Another and more fortunate branch of business into which Boulton entered with Watt and Keir, about the same time, was the manufacture of letter-copying machines. Watt made the invention, Boulton found the money for taking out the patent, and Keir conducted the business. Watt was a very voluminous correspondent, and the time occupied by him in copying letters, the contents of which he desired to keep secret from third parties, was such that in order to economise it he invented the method of letter-copying in such common use. The invention consisted in the transfer, by pressure, of the writing made with mucilaginous ink, to damped and unsized transparent copying-paper, by means either of a rolling press or a screw press. Though Watt himself preferred the rollers, the screw press is now generally adopted as the more simple and efficacious process. This invention was made by Watt in the summer of 1778. In June we find him busy experimenting on copying-papers of different kinds, requesting Boulton to send him specimens of “the most even and whitest unsized paper;” and in the following month he wrote Dr. Black, “I have lately discovered a method of copying writing instantaneously, provided it has been written the same day, or within twenty-four hours. I send you a specimen, and will impart the secret if it will be of any use to you. It enables me to copy all my business letters.”[188] For two years Watt kept his method of copying a secret; but hearing that certain persons were prying into it with the view of turning it to account, he determined to anticipate them by taking out a patent, which was secured in May, 1780. By that time Watt had completed the details of the press and the copying-ink. Sufficient mahogany and lignum-vitæ had been ordered for making 500 machines, and Boulton went up to London to try and get the press introduced in the public offices. He first waited upon several noblemen to interest them in the machine, amongst others on Lord Dartmouth, who proposed to show it to George III. “The King,” said Boulton, in a letter to Watt, “writes a great deal, and takes copies of all he writes with his own hand, so that Lord Dartmouth thinks it will be a very desirable thing for His Majesty.” Several of those to whom the machine was first shown, apprehended that it would lead to increase of forgery--then a great source of terror to commercial men. The bankers concurred in this view, and strongly denounced the invention; and they expostulated with Boulton and Watt’s agent for offering the presses for sale. “Mr. Woodmason,” wrote Boulton, “says the bankers mob him for having anything to do with it; they say that it ought to be suppressed.” Boulton was not dismayed by this opposition, but proceeded to issue circulars to the members of the Houses of Lords and Commons, descriptive of the machine, inviting them to an inspection of it, after which he communicated the results to his partner:--