SIX LECTURES ON LIGHT. 



BY Prof. JOHN TYNDALL, F.R.S. 



PREFACE. 



MY eminent friend, Prof. Joseph Henry, 

 of Washington, did me the honor of taking 

 these lectures under .his personal direction, 

 and of arranging the times and places at 

 which they were to be -delivered. 



Deeming that my home-dud .s could not, 

 with propriety, be suspended for a longer 

 period, I did not, at the outset, expect to be 

 able to prolong my visit to the United 

 States beyond the end of 1872. 



Thus limited as to time, Prof. Henry began 

 in the North, and, proceeding southwards, 

 arranged for the successive delivery of the 

 lectures in Boston, New York, Philadelphia, 

 Baltimore, and Washington. 



By this arrangement, which circumstances 

 at the time rendered unavoidable, the lec- 

 tures in New York were rendered coincident 

 with the period of the presidential election. 

 This was deemed unsatisfactory, and when 

 fhe fact was represented to me I it once of- 

 fered to extend the time of my visit so as to 

 'make the lectures in New Ycrk succeed 

 those in Washington. The proposition was 

 cordially accepted by my friends. 



To me personally this modified arrange- 

 ment has proved in the highest degree satis- 

 factory. It gave mt a much-needed holiday 

 at Niagara Falls ; it, moreover, rendered the 

 successive stages of my work a kind oi grow'/i, 

 which reached its most impressive develop 

 scent in New York and Brooklyn. 



In every city that I have visited, my recep- 

 tion has been that of a friend ; and, now 

 that my visit has become virtually a thing of 

 the past, I can look back upon it with unqual- 

 ified pleasure. It is a memory without a 

 stain an experience of deep and genuine 

 kindness on the part of the American people 

 never, on my part, to be forgotten. 



This relates to what may be called the pos- 

 itive side of my visit to the circumstances 

 attending the work actually done. My only 

 drawback relates to work undone; for 1 carry 

 home with me the consciousness of having 

 been unable to respond to the invitations of 

 the great cities of the West ; thus, I fear, 

 causing, in many cases, disappointment. 

 Would that this could have been averted ! 

 But the character of the lectures, and the 

 weight of instrumental appliances which they 

 involved, entailed loss of time and heavy 

 labor. The need of rest alone would be a 

 sufficient admonition to me to pause here ; 

 but, besides this, each successive mail from 

 London brings me intelligence of work sus- 

 pended and duties postponed through my 

 absence. These are the considerations 

 which prevent me from responding, with a 

 warmth commensurate with their own, to 

 the wishes of my friends in the West. 



On quitting England I had no intention 

 of publishing these lectures, wnd, except a 

 fragment or two, not a line of them was writtes 



