v iii EDITOR'S INTRODUCTION. 



should be disj:>osed to hope that in the future the prog- 

 ress of science will be even more rapid. 



In the first place, the number of students is far 

 greater; in the second, our means of research — the 

 microscope and telescope, the spectroscope, photography, 

 and many other ingenious appliances — are being added 

 to and rendered more effective year by year ; and, above 

 all, the circle of science is ever widening, so that the 

 farther we advance the more numerous are the problems 

 opening out before us. 



No doubt there are other Scientific Series, but it is 

 not believed that the present will exactly compete with 

 any of them. The International Scientific Series and 

 Nature Series are no doubt useful and excellent, and 

 some of the volumes contained in them would well 

 carry out the ideas of the Publishers, but, as a rule, they 

 are somewhat more technical and go into minuter de- 

 tails. 



The names of the Authors are a sufficient guarantee 

 that the subjects will be treated in an interesting and 

 thoroughly scientific manner. 



High Elms, Farnborough : 

 November, 1891. 



