PUBLISHERS' NOTE TO SECOND EDITION. 



The five lectures embodied in this First Series of Half Hours 

 with Modern Scientists were first published as Nos. I. V. of the 

 Univefsity Scientific Series. In this series the publishers have 

 aimed to give to the public in a cheap pamphlet form, the advance 

 thought in the Scientific world. The intrinsic value of these lec- 

 tures has created a very general desire to have them put in a perma- 

 nent form. They therefore have brought them out in this style. 

 Each five succeeding numbers of this celebrated series will be 

 printed and bound in uniform style with this volume, and be desig- 

 nated as second series, third series, and so on. Henceforth it will 

 be the design of the publishers to give preference to those lectures 

 and essays of American scientists which contain original research 

 and discovery, rather than to reprinting from European sources. The 

 lectures in the second series will be (i) On Natural Selection as 

 Applied to Man, by Alfred Russel Wallace ; (2) three profoundly 

 interesting lectures on Spectrum Analysis, by Profs. Roscoe, Hug* 

 gins, and Lockyer ; (3) the Sun and its Different Atmospheres, 

 a lecture by Prof. C. A. Young, Ph.D., of Dartmouth College ; (4) 

 the Earth a great Magnet, by Prof. A. M. Mayer, Ph.D., of Stevens 

 Institute ; and (5) the Mysteries of the Voice and Ear, by Prof. 

 Ogden N. Rood, of Columbia College. The last three lectures 

 contain many original discoveries and brilliant experiments, and are 

 finely illustrated. 



