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Dial and pointer devices|
The earliest Chinese compasses did not have needles. The 'pointers' were shaped as spoons, fish, or even sometimes as turtles. The introduction of a needle was a refinement which made possible a much greater precision of readings on the dials surrounding the pointer.
It was at this stage of develop- ment that we can say that the Chinese pioneered the world's first dial and pointer devices, which are absolutely fundamental to modern science. Needham says of this development: 'Probably by the seventh or eighth century AD the needle was replacing the lodestone, and pieces of iron of other shapes, on account of the much greater precision with which its readings could be taken.' Needles were also used as pointers on computing machines.
The use of a needle in a calculating device can be traced back to at least 570 AD in China; it seems to have been a form of abacus based on compass readings. A description of it survives in a book entitled Memoir on Some Traditions of Mathematical Art, and its accompanying Commentary by Chen Luan (flourished 570 AD). Chen Luan writes: 'In this kind of computing, the digits are indicated by the pointing of the sharp end of a needle. The first digit occupies the Li position, that is, pointing full south; second, or two, is K'un, south-west; the third, or three, is at Tui, full west. . . .' And so on. Chen Luan adds that a digit to be multiplied is indicated by the point of the needle, whereas a digit to be divided is indicated by the needle's (differently shaped) tail.
Needham says of this:
This technique, which would seem to have been a simple sort of abacus-like device, arising out of the old diviner's board, is elsewhere attributed to, or associated with, the name of Chao Ta, a famous diviner of the Three Kingdoms Period (221-65 Al)). But the remarkable thing is that a needle is said to be used as a pointer, and the series starts from full south. It seems hard to believe that this can have had no connection with the magnetic compass, and it must be at least of 570 AD if not earlier. Therefore, dial and pointer devices were in use in China by the sixth century at least, and quite possibly by the third century. Needham rightly points out that these Chinese devices were 'the most ancient of all pointer-readings, and ... the first step' on the road to all dials and self-registering meters.'
The dial and pointer devices upon which we depend in the modern world had originated in China by the third century AD. They were geomantic compasses, used for consultation on such questions as to where a house should be built, or a city laid out. Of course, much was superstition, but at the basis of the practice was the phenomenon of the north-south alignment of the magnetized magnetic needle. The fantastic array of readings which were possible to a geomancer's compass may be seen here, though this is by no means the most complicated. Some are known with forty concentric circles of readings. The outermost circle here marks the twenty-eight lunar mansions. The next circle is marked in the'New Degrees' of 360' adopted for the'circle under Jesuit influence, indicating that this compass cannot be earlier than the seventeenth century. A full description of the readings is obviously impossible in the space available. (Science Museum, London
[ Last edited by changabula at 2007-1-29 08:29 PM ]