39 2 THE BORDERLAND OF SCIENCE. 



stances. c It passed us closely and swiftly,' says Herschel, 

 ' swelling into importance, and dying away with unusual 

 rapidity. The phenomena exhibited by its nucleus 

 and head were on this account peculiarly interesting 

 and instructive, it being only on very rare occasions 

 that a comet can be closely inspected at the very crisis 

 of its fate, so that we can witness the actual effect of 

 the sun's rays on it.' (This was written long before 

 Schiaparelli's theoiy had attracted notice). This comet 

 was also the last observed and studied by Sir John 

 Herschel. The November comet, again, was the first 

 comet ever analysed with the spectroscope. 



It will be remarked, perhaps that where coincidences 

 so remarkable as these are seen to be possible, it may 

 be questionable whether the theory itself, which is 

 based on the coincidence of certain paths, can be 

 accepted as trustworthy. It is to be noticed that, 

 whether this be so or not, the surprising nature of the 

 coincidence is in no way affected ; it would be as 

 remarkable (at least) .that so many events should 

 concur to establish a false as to establish a true theory. 

 This noted, we may admit that in this case, as in many 

 others, the evidence for a scientific theory amounts in 

 reality only to extreme probability. However, it is to 

 be noticed that the probability for the theory belongs 

 to a higher order than the probability against those 

 observed coincidences which rendered the demonstra- 

 tion of the theory possible. The odds were thousands 

 to one, perhaps, against the occurrence of these coin- 

 cidences: but they are millions to one against the 



