Longitude, obliged to leave Paris for Spain. I had observed various
comets, and calculated their orbits. I had, in concert with M. Bouvard,
calculated, according to Laplace's formula, the table of refraction
which has been published in the _Recueil des Tables_ of the Bureau of
Longitude, and in the _Connaissance des Temps_. A research on the
velocity of light, made with a prism placed before the object end of the
telescope of the mural circle, had proved that the same tables of
refraction might serve for the sun and all the stars.

Finally, I had just terminated, under very difficult circumstances, the
grandest triangulation which had ever been achieved, to prolong the
meridian line from France as far as the island of Formentera.

M. de Laplace, without denying the importance and utility of these
labours and these researches, saw in them nothing more than indications
of promise; M. Lagrange then said to him explicitly:--

"Even you, M. de Laplace, when you entered the Academy, had done nothing
brilliant; you only gave promise. Your grand discoveries did not come
till afterwards."

Lagrange was the only man in Europe who could with authority address
such an observation to him.

M. de Laplace did not reply upon the ground of the personal question,
but he added,--"I maintain that it is useful to young savans to hold out
the position of member of the Institute as a future recompense, to
excite their zeal."

"You resemble," replied M. Hallé, "the driver of the hackney coach, who,