Found what seems to be the first electrical analog computer, or at least the first to be described as such. It’s in this 1909 physics journal.
The Arthur Wright Electrical Device for evaluating Formulae and solving Equations wasn’t really a practical device and it wasn’t especially new. Wright was using modified versions of the Wheatstone bridge, which had always been understood as an equation. It can be treated as a proportion or a linear equation depending on whether you measure current or voltage. Wright built a special logarithmic potentiometer to simulate a slide rule on one of the arms of the bridge.
= = = = =
The next item in the journal was more interesting and produced fresh knowledge. It was the first observation of a fact that still remains somewhat mysterious.
When localizing sounds (left vs right), our hearing system operates in two distinct modes. Below 1200 cycles the hearing system is handling the actual waves cycle by cycle, and determining which zero crossing comes first. Above 1200 the system switches to an entirely separate mode, using the intensity difference between the sides. A sound arriving from the left side of the head reaches the left ear directly, while the right ear is ‘shadowed’ by the head like the backwash behind an island in a river. The right ear receives slightly lower intensity, and the ‘shadowed’ sound is also filtered by passing around the hair and face. We learn to recognize the modifications along with the slight intensity difference.
A pure tone around 1200 is on the sharp boundary between the modes, and we have real trouble localizing such sounds. 1200 is a good choice for a boundary because all important speech frequencies are below 1200, but we still don’t know why the system takes the trouble to process time of arrival for low freqs, instead of sticking with the ‘cheaper’ shadow method for all freqs.
= = = = =
Author LT More built a simple but precise phase controller using a tuning fork split into two tubes.
It’s also bridge-like. Here’s a 3d version of the device:
The author moved the tuning fork back and forth so the waves arriving at the ears would slide back and forth in phase.
He tried several different freqs of fork, calculating the wavelength for each sound and sliding the fork back and forth through the same distance each time, which was one wavelength for the lowest freq and several wavelengths for the higher freqs.
In this graph the dotted lines represent the changing phase as the fork slides from one side to the other, and the solid lines represent the average perception of left vs right at this phase setting. You can see how the perceived location gradually slides toward the left (bottom of each graph) as the freq gets higher.
= = = = = START QUOTE:
In figures 8 to 11 inclusive there is a progressively increasing discrepancy between the curves. In all cases I noted changes of direction which followed a sinusoidal curve, but there was besides an increasing difficulty of locating sounds which theoretically should be from the right. When the frequency 1024 was reached in the series, all the sounds apparently came from the left in varying degrees.
The judgement for these high frequencies was also somewhat further confused, as shown by an inclination to locate sounds near the middle or slightly to the left. With practice the regularity of the curves was improved but they invariably showed this decided preference in location.
= = = = = END QUOTE.
The author said that his left ear was better than his right, so he perceived a genuinely centered sound as mainly left. Given the octave freqs he was using, 1024 is a good approximation of the dividing line between the modes.
= = = = =
Meta: 1909 was also a dividing line in tech history. The audion (triode vacuum tube) was invented in 1909.
The audion made electrical analog computers possible. A simple Wheatstone network of resistances can’t perform more complicated calculations beyond the simple proportion, because every change of resistance affects the whole network. It’s like a system of canals with no valves or dams. The whole system always holds the same level no matter where you insert or remove water. With the valve effect of tubes or transistors, you can isolate parts of a calculation, like drawing parentheses in a paper equation. One section can calculate on its own, and then its result provides an input to the next stage without any interference in either direction.
Tube and transistor circuits also made it easy to set up a controllable phase difference, again because stages can be treated as one-way inputs. Two separate oscillators can maintain their own frequencies and phases, and the outputs can be mixed without altering the performance of each input.
Metameta: The tube was one of the few inventions that provided all Creative, no Destruction. It replaced catwhiskers and coherers as a detector, and replaced nothing as an amplifier. The companies that made catwhiskers also made other components, which instantly became more popular and varied as amplification opened up huge new ranges of products. The materials and skills in a coherer transferred directly to audions.
Polistra's Mill 