... ↑

Tis is surely an issue worthy of the attention of researchers with a

synthetic bent – a history of the development of the ideas involved. As

examples of the high value of such work, I cite two cases from Kuhn.

Te frst is from Te Structure of Scientifc Revolutions:

With scientifc observation … the scientist can have no

recourse above or beyond what he sees with his eyes and

instruments. If there were some higher authority by recourse

to which his vision might be shown to have shifted, then that

authority would itself become the source of his data, and the

behavior of his visions would become a source of problems.

Te period during which light was “sometimes a wave and

sometimes a particle” – was a period of crisis, a period where

something was wrong – and it ended only with the develop-

ment of wave mechanics and the realization that light was a

self-consistent entity diferent from both waves and particles.

In the sciences, therefore, if perceptual switches accompany

paradigm changes, we may not expect scientists to attest to

these changes directly. Looking at the moon, the convert to

Copernicanism does not say, “I used to see a planet, but now

I see a satellite.” Tat locution would imply a sense in which

the Ptolemaic system had once been correct. Instead, a con-

vert to the new astronomy says, “I once took the moon to be

(or saw the moon as) a planet, but I was mistaken.” Tat sort

of statement does occur in the aftermath of scientifc revolu-

tion. If it ordinarily disguises a shift of scientifc visions or

some other mental transformation with the same efect, we

may not expect direct testimony about that shift. Rather we

must look for indirect and behavioral evidence that the scien-

tist with a new paradigm sees diferently from the way he had

seen before.

Let us then return to the data and ask what sorts of transfor-

mations in the scientists’ world the historian who believes in

such changes can discover. Sir William Herschel’s discovery of

Uranus provides a frst example. On at least seventeen diferent

occasions between 1690 and 1781, a number of astronomers,

including several of Europe’s most eminent observers, had

seen a star in positions that we now suppose must have been

occupied at the time by Uranus. One of the best observers in

this group had actually seen the star on four successive nights

in 1769 without noting the motion that could have suggested