minutes later than would have been calculated by the previous method. In fact, the emergence that occurred on 9 November was observed and matched the new calculations, prompting Rømer to make a more detailed presentation to the Academy.
© New York Public Library/Science Photo Library
Danish astronomer Ole Rømer (1644–1710) with the tools of his trade.
Unfortunately, most of Rømer’s papers were lost in a fire in 1728, and the only account we have of that presentation is a rather garbled news story, which was translated into English and published in 1677 in the Philosophical Transactions of the Royal Society. But a later document survived and spells out his calculation and the dramatic result that he announced. With the best estimate available to him for the size of the Earth’s orbit, Rømer calculated that the speed of light must be (in modern units) 225,000 kilometres per second. If we make the same calculation, using Rømer’s observations, and plug in the modern value for the diameter of the Earth’s orbit, we get a speed of 298,000 kilometres per second. This is remarkably close to the best modern measurement of the speed of light: 299,792 kilometres per second.
Although not everyone was convinced at the time, the discovery made Rømer’s reputation. He visited England, where he was warmly received and discussed his observations and their implications with such people as Isaac Newton, Edmond Halley and the Astronomer Royal John Flamsteed. They were convinced. In his book, Opticks, Newton mentioned that light takes ‘seven or eight minutes’ to travel from the Sun to Earth. Rømer returned to Denmark in 1681 to become Astronomer Royal and Director of the Royal Observatory in Copenhagen, the spiritual heir to Tycho.
| No. 13 | VITAMIN AT SEA |
There is a particular kind of experiment that is important in everyday life, although it is not usually called an ‘experiment’, perhaps for fear of worrying the people taking part. This is the ‘medical trial’ – a kind of controlled experiment. One of the best examples of a medical trial is also one of the earliest, dating from the 1740s, when James Lind, a surgeon in the Royal Navy, carried out experiments to find a cure for scurvy. The story of scurvy also shows the value of careful experiments and observations, even when it takes a long time for these observations to be explained.
Scurvy is an illness that starts out with a general feeling of being under the weather and lethargy, then develops with spots on the skin, softening and bleeding of the gums, loss of teeth, open wounds on the skin, and eventually death. We now know that it is caused by a lack of vitamin C, but in the eighteenth century nobody knew anything about vitamins. What they did know was that scurvy was prevalent among sailors and soldiers on a restricted diet of dried meats and grains. The problem was highlighted by the fate of the first British circumnavigation of the globe, by a fleet led by Sir George Anson between 1740 and 1744. Out of an initial complement of about 2,000 men, more than half died from scurvy on the voyage. For a growing naval power such as Britain, finding a treatment or preventative for scurvy was a pressing problem.
© St. Mary’s Hospital Medical School/Science Photo Library
The mouth of a person suffering from scurvy, showing swollen and bleeding gums.
Lind was not the first person to suggest that citrus fruits might be used to treat scurvy, but he was the first person to carry out a scientific experiment to test the idea. His ideas about the cause of scurvy were completely wrong – he thought it was caused by a ‘putrefaction’ of the body, which he hoped to treat with acids. On a voyage in 1747, he tested this idea by adding different acids as supplements to the diet of different groups of men afflicted with scurvy. All the sailors ate the same foods, but every day one group had a quart of cider each, one group had 25 drops of elixir of vitriol (sulphuric acid) added to their diet, one group took six spoonfuls of vinegar each, one group had to drink half a pint of seawater, the members of another group each ate two oranges and one lemon a day, and the last group drank barley water and ate a spicy paste. The seawater drinkers were a ‘control’, because they were not given any medicine. Hence the term ‘controlled experiment’. By the time the experiment ended (because the ship had run out of fruit) the health of the sailors given oranges and lemons had improved dramatically; among the other groups, only the cider drinkers showed a slight improvement.
© Science Photo Library
James Lind (1716–1794).
The Royal Navy took note of the discovery, and some captains began to implement a policy of providing ships with a syrup made from oranges, and also with sauerkraut, which had also proved an effective antiscorbutic (from the Latin term for scurvy, scorbutus). Lind left the service soon after this voyage, and although he wrote a book, A Treatise of the Scurvy, which was published in 1753, it was largely ignored. But a second ‘experiment’ was carried out by James Cook on his first circumnavigation of the globe, starting in 1768. His ship carried three tons of sauerkraut. This tasted vile, but Cook persuaded his crew to eat it by a ‘method I never once knew to fail with seamen’. He had the food served at first only to officers, who ate it with the appearance of delight. The men soon petitioned for it to be added to their rations, and the result was that there were hardly any incidences of scurvy.
Although shore-based doctors continued to ignore the evidence, experience had shown the Navy what worked, even if they did not know why it worked. In 1794, lemon juice was issued to sailors on board the Suffolk on a 23-week voyage to India during which nobody died from scurvy. A year later, lemon juice began to be issued to every ship. The juice proved quite palatable, since it was drunk mixed with the sailors’ ‘grog’, a ration of rum diluted with water. This was later replaced by lime juice, which proved even more effective, and, by the middle of the nineteenth century, American sailors had begun referring to their Royal Navy counterparts as ‘lime-juicers’ – later shortened to ‘limeys’ and applied to anyone from Britain.
It was not until the early 1930s that the active ingredient was identified and named ascorbic acid, or vitamin C. Most animals can make their own vitamin C, but monkeys and apes (including humans), guinea pigs and bats are among the few who cannot do so and have to get vitamin C through their diet.
| No. 14 | CONDUCTING THE LIGHTNING |
In the middle of the eighteenth century, there was no way to generate electric currents (see here), but scientists were familiar with the ‘static’ electricity that can be made by friction, for example by rubbing a glass rod with a silk cloth. This is the same kind of electricity that crackles on a dry day when you pull up a sweater made of synthetic material, and a rod charged up in this way will produce a spark when it is touched to another object. These sparks are like miniature lightning bolts, which led people to speculate that lightning might be a form of electricity. The person who took up the challenge of proving this was the American savant Benjamin Franklin. In 1746 Franklin acquired a glass rod from Peter Collinson, a merchant with an interest in science, who was a Fellow of the Royal Society. He carried out a series of experiments with it.
© Print Collection, Miriam and Ira D. Wallach Division of Art, Prints and Photographs/New York Public Library/Science Photo Library
Peter Collinson (1694–1768).