X PREFACE. 



question were now raised for the first time I should 

 advocate the adoption of some considerable modifica- 

 tions. But seeing that no other uniform system is in 

 existence, and that the metrical system has been 

 adopted by nearly all civilized nations, I cannot but 

 regret that my countrymen should retain what is 

 practically a barrier to the free interchange of thought 

 with the rest of the world. The defects of the metrical 

 system are mainly those of our decimal system of 

 numeration, which owes its existence to the fact that 

 the human hand possesses five fingers. If in some 

 future stage of development our race should acquire a 

 sixth finger to each hand, it may then also acquire 

 a more convenient system of numeration, to which 

 the scale of measures would naturally be adapted. 

 In the mean time the advantages of a uniform system 

 far outweigh its attendant defects. 



The adherence to the Fahrenheit scale for the 

 thermometer is even less defensible. It belongs to 

 a primitive epoch of science, when a knowledge of the 

 facts of physics was in a rudimentary stage, and its 

 survival at the present day is a matter of marvel to 

 the student of progress. 



I should not conclude these prefatory words without 

 expressing my obligations to many scientific friends 

 whom I have from time to time consulted with 

 advantage ; and I must especially record my obliga- 

 tion to Mr. Robert Scott, F.R.S., who has on many 

 occasions been my guide to the valuable materials 

 available in the library of the Meteorological Office. 



