THE VALVE OF SCIENCE 311 



consciousness sees directly. This is necessary because without it 

 science could not exist. In a word, psychologic time is given to us and 

 must needs create scientific and physical time. There the difficulty 

 begins, or rather the difficulties, for there are two. 



Think of two consciousnesses, which are like two worlds impene- 

 trable one to the other. By what do we strive to put them into the 

 same mold, to measure them by the same standard? Is it not as if 

 one strove to measure length with a gram or weight with a meter? 

 And besides, why do we speak of measuring? We know perhaps that 

 some fact is anterior to some other, but not by how much it is anterior. 



Therefore two difficulties: (1) Can we transform psychologic time, 

 which is qualitative, into a quantitative time? (2) Can we reduce to 

 one and the same measure facts which transpire in different worlds? 



III. 



The first difficulty has long been noticed ; it has been the subject of 

 long discussions and one may say the question is settled. We have not 

 a direct intuition of the equality of two intervals of time. The persons 

 who believe they possess this intuition are dupes of an illusion. When 

 I say, from noon to one the same time passes as from two to three, what 

 meaning has this affirmation ? 



The least reflection shows that by itself it has none at all. It will 

 only have that which I choose to give it, by a definition which will 

 certainly possess a certain degree of arbitrariness. Psychologists could 

 have done without this definition; physicists and astronomers could 

 not; let us see how they have managed. 



To measure time they use the pendulum and they suppose by defini- 

 tion that all the beats of this pendulum are of equal duration. But 

 this is only a first approximation ; the temperature, the resistance of the 

 air, the barometric pressure, make the pace of the pendulum vary. If 

 we could escape these sources of error, we should obtain a much closer 

 approximation, but it would still be only an approximation. New 

 causes, hitherto neglected, electric, magnetic or others, would introduce 

 minute perturbations. 



In fact, the best chronometers must be corrected from time to 

 time, and the corrections are made by the aid of astronomic observa- 

 tions; arrangements are made so that the sidereal clock marks the same 

 hour when the same star passes the meridian. In other words, it is 

 the sidereal day, that is, the duration of the rotation of the earth, which 

 is the constant unit of time. It is supposed, by a new definition sub- 

 stituted for that based on the beats of the pendulum, that two complete 

 rotations of the earth about its axis have the same duration. 



However, the astronomers are still not content with this definition. 

 Many of them think that the tides act as a check on our globe, and 



