INTRODUCTION 19 



lengthening. All his proofs, however, were in the nature 

 of deductive reasoning, so that it devolved upon his fol- 

 lowers to determine the question by interrogating the 

 physical fact. This they have marvelously well suc- 

 ceeded in doing by mathematical means based on the 

 records of certain ancient eclipses ; but again with disap- 

 pointing results. Says Young (G. A., p. 105) : 



At present it can only be said that the change, if any has 

 occurred since astronomy became accurate, has been too small 

 to be detected. The day is certainly not longer or shorter by 

 i-ioo of a second than in the days of Ptolemy, and probably has 

 not changed by i-iooo of a second. 



What, then, in veiw of these indubitable disproofs, 

 do you say should be done with Newton's tidal theory! 

 Should it not be jettisoned at once and all haste made to 

 find a better? 



THE COMETS 



These objects remain as great a mystery to men of 

 science of the twentieth century as to Newton and his gen- 

 eration. It is true that some new information has been 

 gleaned from the spectra of comets, and also from a crit- 

 ical study of their orbital vagaries ; but as to their origin 

 and nature, and the causes of the peculiarities exhibited 

 by their tails, practically nothing has yet been satisfac- 

 torily determined. Young sums it up by saying (Art. 

 737) : " We have little certain knowledge on the subject." 



THE SOURCE OF THE SUN'S HEAT 



Newton sought to explain the light and heat of the 

 sun by supposing the original chaos to have been com- 

 posed of two main kinds of matter, luminous and non- 

 luminous, and then picturing the Creator as segregating 

 the first kind into the central body that we call the sun, 

 and molding the rest into the earth, moon and planets. 

 A century later Laplace postulated incandescence for his 

 nebula and thence derived, not only our glowing luminary 

 but the planets, also, in an original state of fusion. 



