Six Months in Ascension
Thanks in part to his intrepid wife, David Gill made the observations that metered the 19th-century solar system
Malignant Fate, or an Ill-Placed Volcano
After a week of setting up the equipment, David prepared to start
his campaign of observing Mars. He was in for a shock: Although
every day was brilliantly sunny, every night was cloudy! Isobel wrote:
Oh! those weary weeks. Fearful of losing a single hour of
star-light during the night, we watched alternately for moments of
break in the cloud, sometimes with partial success, but more
frequently with no result but utter disappointment, and the mental
and physical strain … grew almost beyond our strength.
The torrid heat and dust of the daylight hours only added to
their sullen mood, and tempers began to flare. One night David
remarked it was almost as though a malignant fate brought the cloud
over them; he could almost see clear skies away on the horizon.
Isobel immediately announced that she was going to take a long walk
across the lava beds to see whether the sky was clearer elsewhere.
David was aghast. It was madness to traverse the broken surface in
the dark, and David couldn't leave the telescope in case the sky
cleared. But Isobel was adamant. David woke up one of their helpers
and told him to prepare a lantern, food and water, and accompany
Isobel on her 2 a.m. walk. Regrettably, this worthy's thoughts that
night have gone unrecorded.
Whatever the impetus for her walk, Isobel had found the solution.
The skies were indeed clear just a mile or two away. The Gills had
been the victims of what today would be called an orographic
cloud—one caused by air forced upward by a topographical
feature. Their site had been downwind from the main volcanic peak on
the island, and changes in the nighttime air produced a cloud
streaming out from the peak. David would have to move the
observatory away from town. And therein lay the rub! No means
existed for moving 20 tons of delicate instruments across the
smashed terrain, or "clinker." Finally one local pointed
out a small, clear beach, later to be named Mars Bay, on the
southwest coast. Workers loaded the equipment onto a naval steamer
and brought it ashore at the beach.
The Gills camped for the next several months in two tents pitched on
the lava beds ("I am at a loss to convey . . . an idea of what
sort of flooring clinker makes." wrote Isobel). Their two
helpers fetched food from town each day and brought water by boat,
swell permitting. There were setbacks. The assistants had pitched
the tents incorrectly, and a passing rainstorm soaked people and
equipment. Hordes of "musquitoes" soon followed. Later,
David fell and injured his knee on the clinker and suffered mild
sunstroke. But through it all, the determined team got the data they
came for, David at the telescope, Isobel recording the numbers he
Not until they returned home and analyzed the measurements did they
learn that they had been successful. David's calculations produced a
solar distance of 93.08 ± 0.16 million miles, the most
accurate determination up to that time and one that compares well
with today's value of 92.9558. The young Scotsman became famous and
was subsequently appointed Her Majesty's Astronomer at the
Admiralty's southern Royal Observatory in Cape Town, where he
flourished and eventually became Sir David Gill.
David died in 1914, and Isobel in 1919. They are buried side by side
in the ruins of the 14th-century Cathedral of St. Machar in their
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