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Miss Roemer's remark about the dread that some people have as to any connection with the police, is true to a limited extent only. It is true only of the ignorant mind, not of a man presumably well-to-do and properly educated. I do not understand why the man to whom this letter was addressed has not made himself known. The only explanation is that there was no such man!"
Freed from all hypothetical by-thought, Roemer's observation tells us, first, that the time taken by a flash of light travelling from a cosmic light-source to reach the earth varies to a measurable extent, and, secondly, that this difference is bound up with the yearly changes of the earth's position in relation to the sun and the relevant planetary body.
Roemer's first observation was made when the earth was in the part of its orbit nearest Jupiter. About six months afterwards, the earth being then at the opposite side of its orbit, when the little moon ought to have made its hundredth appearance, it was found unpunctual, being fully 15 minutes behind its calculated time.
Roemer's discovery of the progressive motion of light, though denounced by Fontenelle as a seductive error, and not admitted by Cassini, at length forced its way to universal acceptance. Next it was necessary to obtain correct ideas of the dimensions of the solar system, or, putting the problem under a more limited form, to determine the distance of the earth from the sun.
"It would be horrible, horrible and yet I do not know what to think." There was silence in the room for a moment. Miss Roemer's head drooped again and her hands twisted nervously in her lap. Muller's brain was very busy with this new phase of the problem. Finally he spoke.
We can here leave out of account the fact that Roemer's reasoning is based on the assumption that the Copernican conception of the relative movements of the members of our solar system is the valid conception, an assumption which, as later considerations will show, cannot be upheld in a science which strives for a truly dynamic understanding of the world.
Was there any other reason beyond the dead man's past that would render your guardian unwilling to have you marry him?" Again the slow flush mounted to Eleonora Roemer's cheeks and her head drooped. "I fear it may be painful for you to answer this," said Muller gently, "and yet I must insist on it in the interest of justice."
Owing to an error in the determination of the earth's distance from the sun, the velocity assigned to light by both Roemer and Bradley is too great. With a close approximation to accuracy it may be regarded as 186,000 miles a second. By Roemer's discovery, the notion entertained by Descartes, and espoused by Hooke, that light is propagated instantly through space, was overthrown.
For the change of aspect which becomes necessary in this way does not invalidate Roemer's observation as such; it rules out only the customary interpretation of it.
What matters to us here is the validity of the conclusions drawn from Roemer's discovery within the framework of thought in which they were made. Boiled down to its purely empirical content, Roemer's observation tells us solely and simply that within the earth's cosmic orbit light-flashes travel with a certain measurable speed.
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