vi PEEFACE. 



dall, and other assistants at South Kensington, who have helped 

 me to do the work ; (2) to my colleagues, Professors Perry, 

 Howes and Farmer, and Professor Poulton and Dr. Woodward, 

 who have so freely given me information 011 several of the points 

 touched upon in the later chapters ; (3) to Professor Kayser, Sir 

 William Crookes, .Professor A. Schuster, and Dr. Preston, who 

 have been good enough to look over the portions referring to their 

 researches ; and (4) to the officers and council of the Royal Society 

 and to Messrs. Macmillan, for placing at my disposal some of- the 

 illustrations. 



NOBMAN LOCKYER 



Solar Physics Observatory, 

 South Kensington, 

 January 9, 1900. 



