TTNDALL AND HIS AMERICAN VISIT. 505 



permeates everything. All science seems worked with reference to it. Tyndall 

 not only assumed it, but it was the foundation of his philosophy. While I was 

 with him the other day Spencer started the point of using the term persistence 

 of force rather than conservation. They had quite a spurt over it. But to-day 

 Huxley used the term persistence of force. The experiments last night were, 

 first, testing oxygen and hydrogen separately; second, exploding them together; 

 third, bursting iron bottles by freezing; fourth, exhibiting the formation of crys- 

 tals by the electric light in a vacuum ; fifth, formation of an immense spectrum 

 on a screen, absorption of its different parts by colored glasses; and sixth, regela- 

 tion of iron. He had splendid diagrams of the glaciers, but hardly referred to 

 them. He was not still a moment, but bending and twisting in all possible 

 shapes as if he had the St. Vitus dance twisting his legs together, bending 

 down to the desk, and working and jerking himself in all possible directions. 

 Everybody was kept awake, entertained, and instructed. It was a work of enthu- 

 siasm. 



One of the consequences of that first interview with Tyndall 

 appears in the following extract from a letter of my brother's 

 written to Mr. Spencer in March, 1863. He says : " I received the 

 advance sheets of Prof. Tyndall's book on Heat, and beg of you to 

 express to him my sincere thanks for the kindness. The Apple- 

 tons will issue it at the earliest moment, the cuts being already 

 nearly all re-engraved. It is a very fascinating and altogether 

 remarkable book, and it will be a pure pleasure for me to work 

 for its circulation. It can not fail to have a good sale." 



A letter of Prof. Tyndall's to my brother relating to the publi- 

 cation of his work on Heat, and bearing date April 29, 1863, is the 

 earliest one in my possession. It is as follows : 



MY DEAR SIR : As soon as I received the letter with which you kindly favored 

 me some months ago, I communicated at once with Mr. Longman and requested 

 him to forward you the separate sheets of my work on Heat according as they 

 appeared. I intended to accompany the sheets with a letter which should ex- 

 press my desire to leave the management with the Messrs. Appleton entirely in 

 your hands, but I have been so knocked about sometimes so ill, sometimes so hard 

 worked, and sometimes engaged so far away from London that I have delayed 

 thus far to write you. My friend Spencer called to see me a few days ago, and 

 from him I had the great gratification of learning that the book has interested you. 

 Indeed, he read portions of letters from Mrs. Youmans and yourself which gave 

 me very great pleasure. Since the appearance of the work I have had communi- 

 cations from many of my eminent Continental friends regarding it, and they, I am 

 happy to say, concur in your opinion. A French translation of it has already 

 been commenced. I can assure you that I have spared no labor to render a diffi- 

 cult subject intelligible, and it gives me great pleasure to find that I have, at least 

 in some measure, succeeded. 



I am now giving a short course of lectures on Sound at the Royal Institution. 

 If I have time I may throw them into a readable form. I have for some time 

 entertained the idea of publishing my lectures gradually and of afterward collect- 

 ing them and fusing them into a book on general physics. But the time necessary 

 to the proper accomplishment of the task deters me almost from undertaking it. 

 However, it may perhaps be executed by slow degrees. 

 VOL. XLIV. 39 



