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This was a book that aroused immediate curiosity, bearing an obvious word play title affiliation to Dava Sobel's, 'Longitude'. Apart from that, the two books are quite different, in more ways than their 90 degree, geographical dissimilarity. The Carter's write an interesting account of how since the 17th century, there was an unidentified anomaly in the positions of stars. Measurements from Greenwich differed slightly from those made in Paris and Berlin. Experimental error was blamed. When at last, in the 19th century, American observatories became sufficiently well equipped the effect was even more pronounced, either the stars were in the wrong place or the latitudes of American observatories were downright wrong. In reality, European observatories were too close together and it was not until geographically more widespread observatories were founded that the dual 12 month and 14 month periods of polar motion could be resolved. The effect was slight, amounting to a fraction of a second of arc in latitude. In 1888, the German astronomer, Karl Küstner, proposed that a variation in latitude existed but it was not until about four years later, in 1892, that the American amateur astronomer, Seth Carlo Chandler, concluded that there were in fact two simultaneous variations in latitude, with periods of ten and fourteen months that accounted for the variation. Chandler spent more than twelve years on his quest, battling against his academic superior, Simon Newcomb. Chandler was proved correct, on the basis of altitude measurements taken with an instrument of his own design, the almucantar. For his work he was awarded the Gold Medal of the Royal Astronomical Society in 1896 and Küstner in 1910. The variation in latitude is now a proven phenomenon (polar motion), wherein the slight imbalance of the earth due to the variable effect of tides, seasonal air mass movement and even the variable mass of tree foliage in the northern hemisphere causes the earth's spin axis to move around the geographical poles within a radius of about 20 feet (6metres). Even this is important to Geodetisists, as it affects global positioning to a small but measurable degree. The Carter's elucidate an obscure subject of which the majority of us are unaware. Nevertheless, it was, as they say, the first contribution to world astronomy that Americans were able to make. Their insight into 19th century American astronomy and its infighting is interesting and informative and I recommend their book. There are two main
criticisms. From the outset, the Carters insist on comparing measurements
in Imperial and Metric. I don't know if this was left to the publisher,
but we have measurements in inches (centimeters) and yards (meters),
back and forth that have little correlation. After a few pages this
becomes irritating…and it goes on throughout the book getting progressively
sillier, with feet (meters) and so on. Secondly, 'Astronomer Royal'
is a title and deserves capital letters, and Edmond Halley has two 'l's.
I understand that the Carter's did originally use capital letters for
Astronomer Royal but the publisher changed this. The spelling mistake
has been corrected in the latest printing. Kevin Kilburn, F.R.A.S. |
