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By Root 407 0

until the fall of 1912. But by then his refashioned spectrograph was operating two hundred times faster than the instrument's original specifications, allowing him to slash his long and tedious exposure times. With his modifications in place, he could at last try for the spectrum that he had so long sought. It was a tantalizing goal, not only scientifically, but personally as well. Two years earlier Lick director Campbell had spoken at Yale University and specifically observed that “there is no more pressing need at present than for a greatly increased number of nebular radial velocities.” To beat Campbell at his own specialty—radial velocities, how fast celestial objects move either toward or away from us as if traveling along a radius—would be sweet triumph indeed for Lowell Observatory loyalists. No one had yet gauged the speed of a spiral nebula. That required a spectrum with more detail than had ever been previously obtained or even deemed possible.

Slipher carried out his first measurement on September 17. It took a total of six hours and fifty minutes for the extremely faint light to fully register. “It is not really very good and I am of the opinion that we can do much better,” he soon relayed to Lowell, “but in view of the results got elsewhere of it generally with much longer exposures, it seems to me encouraging and I mean to try it again.” The spectrum was very tiny, a mere centimeter long and a millimeter wide. The photographic plate itself was barely eight centimeters long, but there was just enough room for Slipher to write “Sept 17 And Neb” on the top of the glass to indicate his target had been the Andromeda nebula.

Gale's Comet required his attention for most of October, so he was not able to get back to Andromeda until November 15. The weather was fair with some clouds, but the wind was strong. He started the measurement at seven that night. Being winter, it was already fully dark, and he worked into the early-morning hours. The plate was exposed for eight hours and was left in the spectrograph, shutters closed, so the following night he could align the telescope once more upon his target and continue the observation for another six hours. By taking the longer photographic exposure and narrowing his slit, he saw some improvement in the spectrum when compared with the one taken in September.

He returned to the problem on December 3 and 4, when the Moon no longer rose at night to interfere with his observation of the dim nebula. This time, Slipher scribbled in his workbook that the transparency of the air was “very good,” underlining it for emphasis. Over the two nights he was able to gather his sparse photons for a total of thirteen and a half hours. The only problem that arose was a troublesome clock drive that took fifteen minutes to fix.

When carrying out these observations, the interior of the wooden dome at times resembled the movie version of a mad scientist's laboratory, with high-voltage induction coils sparking and sputtering by the side of the telescope. A row of old-fashioned Leyden jars provided the ignition. It was a wonder that Slipher didn't electrocute himself. This Rube Goldbergian contraption vaporized samples of iron and vanadium, whose light then served as a calibration for Slipher's measurement. The spectrum of these elements, at rest within the dome, could be compared to the spectrum of the nebula rushing around in space; the difference between the spectra determined the nebula's speed.

Since each spectrum that Slipher produced from Andromeda was so tiny, he needed a microscope to measure how much the spectral lines had shifted, compared to their positions on the calibrated standard. The more the shift, the higher the velocity of the nebula. The microscope had been with Lowell in Boston temporarily, and Slipher didn't get it back until mid-December. But once the scope arrived he couldn't resist taking a quick peek at the Andromeda plates he had so far. There were “encouraging results or (I should say) indications,” Slipher reported to Lowell, “as there appears to be an appreciable