Monday, July 27, 2009

Dr. Priestley's Slide Rule

I mused about whether Joseph Priestley, eminent natural philosopher that he was, ever had a slide rule.  While I was at the Priestley House in 2004, I asked the docent, Brooke Dearman, if they had any information to that effect.  Wouldn't you know, the following day she informed me that on the Inventory of Dr. Priestley's Laboratory in 1791 was the listing of a slide rule.  Just in case you don't remember, this is the very same Laboratory that was burned to the ground during the Birmingham Riots of the same year. So, in fact, this is a list of the items that were destroyed when the Laboratory was destroyed.

This Inventory appeared first in the Birmingham Weekly Post in 1890, and was subsequently reprinted as an Appendix in Scientific Correspondence of Joseph Priestley by Henry Carrington Boulton in 1892, and then reprinted again in the reprinting of Boulton's book by the Kraus Reprint Co., New York, in 1969. I've referred to this book before. If you are seriously interested in studying about Priestley, it is a good book to have for reference.

There it is on page 229 under the category of Mathematical Instruments, "A Sliding Rule of the best construction" and on the next line "A Navigation Sliding Rule".  So, now we know that he had two "Sliding Rules". 

But, is there anything else we can learn or conjecture about these sliding rules.  During this period of time, from 1780 to 1790, Matthew Boulton, the famous engineer and industrialist,and his partner of James Watt,  who were both friends of Priestley's and also members of the Lunar Society, had produced a "Sliding Rule" at their Soho Manufactory called a "Soho" ruler in about 1775. This was specifically designed for the engineers' use at Soho. James Watt, earlier in his career was a scientific instrument maker and was quite familiar with the sliding rule.  As best as I can tell at this time the Soho sliding rule had A B C D scales, the  A B and C  scales were double decade scales so that squares and square roots could be computed rapidly, and the D scale was a linear scale. 
There also appear to have been some French slide rules being produced at this time also.

So, it is not clear which exact type of sliding rules Priestley had in his Laboratory. He certainly had access to the Soho sliding rules through Boulton and Watt.  Additionally, we know that Boulton supplied many other instruments and items of need to Priestley's laboratory.  Any information on this would be greatly appreciated.

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