Re: 1638 Letter from Oughtred to Allen
Tom and Lu Wetmore
I can only say maybe. The device in question is a cross staff with log lines. Whether both the staff and the transverse had the same log lines is open to question. I believe the quote only means Oughtred has not yet seen what Allen has done on the device so far. With a single set of log lines the cross staff is usable with compasses. These log lines were all two decades long, making this possible.
This is only one piece of communication between Oughtred and Allen about this device. This letter comes after Allen has already etched some scales. Allen had sent Oughtred impressions of those scales by inking the scales and 'printing' them on paper. Oughtred is sending instructions for follow on work. So we are seeing the cross staff through a small window in the middle of its development. I want to reexamine that printing to see if the log lines are already on it. If they are I think we could assume that the staff already had the log lines and Oughtred is adding them to the transverse. But if so it seems he would have instructed Allen to make them the exact length of the scales on the staff. Since the transverse is shorter than the staff this instruction would be very important.
This isn't enough for me. I want this cross staff to be usable as a two rod slide rule, but I don't think there is enough evidence here.
This could imply logarithmic lines, or it could mean that he is helping Allen compute etching locations for other scales by computing locations as parts of 100000. Though I agree this seems most applicable to log lines.
As I say, I want this cross staff to be used in this way, and the letter is suggestive of it, but I don't see it as conclusive.
I don't believe this. Have you read Forster's "The Circles of Proportion and Horizontal Instrument, Both Invented and the uses of both written in Latin by Mr. W. O. [William Oughtred], Translated into English and set forth for he publique by William Forster"? In the forward of this book Forster describes his visit with Oughtred in 1630, and that at that time Oughtred showed him both linear and circular slide rules that he had had in his work room for years, and his instructions, written in Latin, for using them, were fully developed by then. For me this puts the invention of the slide rule well back into the 1620s in Oughtred's back room. This is a second source that gives Oughtred priority. I know you believe that priority should go to the person who publishes first, but I am not as firm on that point.
I believe Oughtred deserves priority. I am not swayed by Delamain. But I concede that there is not enough evidence to prove the inventor. This argument seems similar to the one about who wrote Shakespeare's plays. Maybe we can never know, but we can appreciate that such masterpieces of the English language exist.