202 Baron Fourier's Historical Notice 



dividual who protected his youth, and directed him in the study 

 of the sciences, — to him from whom he received the first coun- 

 sel, the first instructions, and the first marks of interest. 



It is honourable to attract by brilliancy of talent a numerous 

 auditory, to propagate important knowledge, and discoveries of 

 national utility ; but to distinguish in a crowd a youth unpro- 

 tected, — to recognize in him the first marks of genius, — to pre- 

 dict what his country and the sciences would one day owe him, 

 — to welcome, to encourage, and to instruct him, is, in the order 

 of good deeds, one of those that should occupy the first place, 

 and there is none more becoming a man of letters. 



The first researches of M. Breguet had for their object that 

 part of his art which relates to civil purposes ; and he after- 

 wards brought to perfection that which concerns the sciences. 



The question of the measure of time which the moderns 

 have so well resolved, consists in producing a rotatory motion 

 perfectly uniform, which renews and preserves itself without 

 any change. The moving body is submitted to two opposite 

 actions : the one, which is the moving force, constantly tends 

 to accelerate the motion : the other^ which is opposed to it, de- 

 stroys at each instant with a rigorous accuracy all the excess of 

 the new impulse, so that the velocity remains always equal to 

 itself. This perpetual collision is the dynamical principle com- 

 mon to all instruments which measure time. 



But how many difiiculties must be overcome to gain this ob- 

 ject ! We must, in some degree, withdraw the instrument firom 

 the action of those external causes which tend to disturb the 

 uniformity of its motion. The friction of the different parts 

 continually changes their form, and may change the velocities. 

 Changes of temperature, too, render their dimensions and the 

 elastic forces variable. If the common use of the instrument 

 expose it to irregular agitation, or to great changes of position, 

 there arises from it other causes of inequality. The resistance 

 of the air is not constant, but varies with its density. Art has 

 opposed to one another all those causes of perturbation, so as 

 to make them reciprocally destroy each other. The mean ef- 

 fect of changes of position becomes insensible ; variations of 

 temperature compensate each other ; external and accidental 

 agitations do not alter the motion, and they are used to main- 



