JF Ptak Science Books  Post 2353

That is a provocative title, or chapter heading, but that’s how it appears in a pamphlet I’m reading right now, a juicy thing that can lead to a memory palace of ideas…until you start reading the para below the head, when things get both more crystalline and fuzzy.

John Alexander Henderson, a lightning calculator and professor of math at Delaware College in New York, produced this sprightly pamphlet eponymously titled Henderson’s United States Intellectual and Practical Lightning Calculator, the Unity and Decimal Method, which he published in St. Louis in 1879. (It is followed a few years later in another edition with a hundred new pages.) 

What Mr. Henderson is getting at is a calculator for reducing a date to find out the day of the week a particular date falls on, from the 1st century to the 99th.  On the back cover of this pamphlet he provides a tickler for this enumerating device, which is explained in another publication (Henderson’s United States Unity and Decimal Method of Calculating). 

And so in order to calculate the day of the week on which, say, November 26, 2014, occurs you would you the dial above as follows, but first an explanation of what is on the dial face: