I just solved “Einstein’s Riddle” in the back of differential (LTD) Stirling engines for the past 15 MAKE, Volume 17 (“Aha: Puzzle This”). I thought years, like the “Teacup Stirling Engine” from MAKE, I would share the creative process that ensued. Volume 17.

The first thing I took into account: there are 25 This type of engine was the result of a friendly pieces of data involved. The second step: how do competition between two ingenious professors, you apply logic with the data given? Knowing that to Prof. Ivo Kolin (University of Zagreb, Croatia, thermo-solve the puzzle I would basically be doing TRUE or dynamics) and Dr. James R. Senft (University of FALSE variables, I devised a plan to make movable Wisconsin, mathematics) starting in 1983. Kolin’s boxes with text for each of the 25 data pieces. first engine ran at a temperature differential less

I wrote out each piece of data on paper and cut than 100°C (180°F), which was a feat at the time. them out. Next I took a digital photo to bring them By 1990, Senft’s “P- 19” engine, the design basis of into Photoshop and make each piece of data its own most LTDs built today, including “Teacup,” could run layer. I made 5 columns, starting with house color. on a temperature difference, hot side to cold side,

The final step was to go through the questions in of 0.5°C — less than 1°F! the same order from beginning to end. If you ask For this reason, it has been suggested (baileycraft. a question and answer TRUE, continue to the next com/ senft.htm) that these engines be referred to question. If FALSE, adjust the tiles until the question as Senft Stirling engines. And yes, there have been = TRUE, then start at question 1 and repeat. If you get consumer applications proposed ( makezine.com/ to the last question and it’s TRUE, end the program go/senft). These engines are described in loving — you just answered the riddle. detail in Dr. Senft’s book, An Introduction to Low

The entire process, including cutting and importing, Differential Stirling Engines (Moriya Press, 1996). took around 40 minutes, including 20 minutes on the Thanks again for a wonderful magazine. Even actual logic. The getting there is the best part. better than the Popular Mechanics of my youth!

—James Uncapher, Plainfield, Ill. —Bill Dreschel, State College, Pa.

MAKE 17 is awesome. I’m a huge steampunk fan and your team did a great job with this issue. Also, I’ve been catching Make: television when I can — really great job there, too.

Gareth Branwyn’s article “William Blake: Patron Saint of Makers” was superb — one of my degrees is in English (the other industrial engineering), and this article hit both sides of my brain.

—James Floyd Kelly, Atlanta, Ga.

Love the magazine! What a great resource. It is important to know where ideas originate, I think, and to give credit where credit is due. People all over the world have been building low temperature

MAKE AMENDS

A handful of errors made it into MAKE, Volume 17:

In “The ‘Discreet Companion’ Ladies’ Raygun” we regrettably misspelled the name of photographer John Keatley.

In “The Florence Siphon Arabica Brewing & Extraction Apparatus,” on pages 65–66 all references to 4mm tubes and holes should be 7mm.

The name of designer Silvia Bukovac Gaševic was misspelled on page 90. We regret the error.

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