6(5 Chapter V 



I 



of these remains constant over a large series of curves. It is very 

 improbable that such a constancy is merely fortuitous. 



The classical example of this principle was first put forward by 

 Laplace with reference to the direction of the orbits of the members 

 of the solar system. In its up-to-date form it is as follows : "...the 

 tale of the asteroids has now approached five hundred and out of this 

 huge number of independent planetary bodies there is not a single 

 dissentient in the direction of its motions. Without any exception 

 however they all perform their revolutions in the same direction as 

 the sun rotates at the centre. When this great host is considered 

 the numerical strength of the argument " (that the arrangement is 

 referable to a physical cause and is not purely fortuitous) "would 

 require about 150 figures for expression*." Even before any of the 

 asteroids were discovered, Laplace considered the argument a strong 

 enough one to justify the nebular hypothesis. 



It may be urged that the analogy is not sound, for it looks like 

 a comparison of something qualitative with something quantitative. 

 The planet must go round either clockwise or counter-clockwise, 

 whereas all that we can say of n is that it remains constant within 

 the limits of 2'45 and 2'5o over all the curves which have been deter- 

 mined for human blood. Closer than that we cannot determine it. 

 Even so, the solar system will not fail us for an example. The orbits 

 of the seven planets lie in the same plane within 9 of arc. The 

 chance against this taking place without a physical explanation is 

 about 10,000,000 : 1. This was Kant's argument in favour of the 

 nebular hypothesis. 



We can calculate the value of n on any one of the curves of which 

 we have been speaking to within about four or five per cent, and 

 within these limits it is the same for all. I leave it to some 

 mathematician to say what the chances may be of n being the same 

 within four per cent, in a dozen curves, when, if it were a perfectly 

 fortuitous mathematical expression, it might be anything between 

 zero and infinity in any given case ; but I have probably said enough 

 to convince the reader that since n remains so constant it is probably 

 the expression of some definite physical fact. 



It is clear that any theory which applies to the formation of 



oxyhaemoglobin must also apply to CO-haemoglobin. Therefore the 



equation may be put to the further test of applying it to the parallel 



data with regard to the dissociation of carboxyhaemoglobin in the 



* Quoted from the Earth's Beginning by Sir Robert S. Ball, 1909, p. 316. 



