Slide Rule

Slide rule¹ – This piece could be about that indispensable, essential and interesting scientific device that used to hang on the belt of every engineering or science university student in the pre-1960 era. But it’s not. It’s about an encounter with a most interesting man, and it might reveal a tiny sliver of forgotten history. The man is Arthur Frederick Eckel² (1893 – 1960). Nearly all of us who are now in our nineties remember only his last name in connection with the magnesium marvel, the Pickett and Eckel slide rule.

After the war, marriage, and the university I began my working career in the summer of 1951 at the North American Aviation facility in Downey, California. We were engaged in a very large research and development project aimed at producing a long range intercontinental air-breathing unmanned missile for the cold war. At that time, before satellites, the uncertainty of where Russia was exceeded 10 miles so these missiles were to be armed with very large hydrogen bombs to assure the distant target’s destruction. My work was involved with the star tracking guidance system; optical telescopes, gyros and very high precision mechanical parts.

The dozens of engineers and scientists at Downey were assigned desks in a very large hanger -- no cubicles or walls. I was fortunate to have a desk next to an older gentleman introduced to me as “Dr. Eckel.” Only after having known him for many weeks did I finally learn that he was one of the inventors of the famous Pickett and Eckel slide rule. That, I certainly knew about. I was impressed.

Dr. Eckel had been hired by North American because of his extensive experience in precision machine work, not for his knowledge of slide rules. The top managers were making an oral history of some of his early work through detailed interviews. He was depended on for advice in developing the methods needed for creating the inertial navigation system and the pointing mechanisms for the star tracking telescopes. I was lucky to have actual hands on work on those devices. I was also lucky to be able to have conversations with Dr. Eckel, my desk neighbor, reminiscing about some of his early efforts in the field of astronomy.

At North American his advice was especially needed in making what was called a ‘lead screw.’ This threaded item was only about 6 inches long and about an inch in diameter. It had a very fine thread machined along its length. As it turned in the final star tracking assembly it pointed the small telescope at the selected stars with an accuracy of better than one second of arc. That is hard to do. Some of Eckel’s advice included placing the screw in a vertical position for machining because of the effect of gravity; even with that one inch thick rod an imperceptible sag during the machining would introduce error. And he advised that the final polishing of the threads had to be done with ground chicken bones. Sounds crazy but he was serious.

In casual conversations he told me of his early career. As a young machinist he had been employed in the shop in Pasadena that was constructing the 100 inch Hooker telescope for Mt. Wilson. This was to be the instrument that Hubble used to discover the universe. As some may know the original funding given to George Ellery Hale came from a man named Hooker, hence the name, but later funding to finish the project was given by Andrew Carnegie. The work began in 1912 and was completed in 1917. During this period Eckel was responsible for making the large bull gear that rotated the telescope on its equatorial mount as well as other precision jobs.  Eckel told of the day he met Carnegie. “I was in the machine shop working at a lathe. Carnegie came in on an inspection tour of his project and came up to me at the lathe. Rather than questions about the work he was mostly intrigued by the curls of metal on the floor that came from the lathe cutting tool.”

He also told the story of his difficulty in making the lead screw for the device that produced the very large diffraction grating at Mt. Palomar. It was made in four sections, each 5.5 by 7 inches, to solve the problem of wear on the engraving tool. The excessive length that might be needed for the screw that controlled the engraving tool if they tried to make the full 14 inch surface at one go was an impossibly difficult problem. No grating engine of this size had ever been made before. This large grating surface was necessary to take full advantage of the light gathering capability of the Hale telescope’s 200 inch diameter. Nearly every observation made by large telescopes involves the use of a diffracting device to examine the spectral characteristics of the observed object. For those not familiar with the history of large telescopes the Hale instrument dominated astronomical research from it inauguration in 1948 until the Keck was put into service in Hawaii in 1993. The earlier Russian BTA-6 which was larger never achieved successful operation.

I hate to end on a negative note but the story does have a coda and it’s not so nice. Eckel had three children. I was able to track down some of his relatives and eventually found a grandson in North Carolina. I placed a call to the business where he worked and spoke to his boss. The grandson was busy and couldn’t come to the phone. I explained my mission and left a message for him to call. I wanted to give him the information that I had which I presumed he would never have heard. He did not call back and I can’t find my notes which would allow me to repeat my efforts.

¹In about 1620 E. Gunter and W. Oughtred of Cambridge produced what today we would recognize as a slide rule computing device based on the work of John Napier. Wikipedia notes that H. Coggeshall designed a slide rule device for the measurement of timber in 1677; however, Samuel Pepys notes in his journal that he came into possession of a slide rule device for computing ship construction materials, including timber, much earlier – about 1666.   

                        

 ²Born in Illinois, USA in 1893 to Albert Edward Eckel and Ida Lill Wilson. Arthur Frederick Eckel married Myrtle Elizabeth Scott and had 3 children. He passed away on 22 Jun 1960 in Burbank, Los Angeles, California, USA.