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everything, down to the minutest detail, was prepared with nicety; and the experiments were consequently performed with a precision unequaled by the manipulation of an accomplished conjurer.

The qualities which characterized his lectures were reflected, as far as possible, in his writings. There was the same clearness of thought, the same vigor of expression. Most of his writings were, indeed, reproductions or developments of his lectures; witness his popular works on Sound, Light, and The Forms of Water. His best-known book, Heat considered as a Mode of Motion—in which he presented, thirty years ago, an admirable exposition of the phenomena of heat in accordance with the dynamical theory—may be accepted as typical of his felicity of expression and readiness of illustration.

It was these rare gifts as an interpreter of science which first drew the attention of American readers to Prof. Tyndall, and which finally led to his visit to this country in 1872. Many now living will recall that event and the impulse given to American science by the brilliant course of lectures which he delivered in our chief Atlantic cities.

Having been asked to prepare a brief account of this visit, and being assured that it will be of interest just now to the readers of the Monthly, I have decided to comply with the request. I am enabled to do this by the aid of documents and letters left by my lamented brother, E. L. Youmans, who for many years enjoyed the friendship of Prof. Tyndall, and was in frequent correspondence with him.

Tyndall's first book. The Glaciers of the Alps, was brought out here by Ticknor and Fields in 1861. All who read it were fascinated by the clearness and beauty of its style and the ease with which its facts and principles could be understood.

The year following, my brother made his first visit to England and while in London it was his good fortune to be introduced to Tyndall. In a letter of September 25th he writes:

I went with Spencer at his request to see Tyndall respecting the publication of his forthcoming book. He was at the Royal Institution, where his researches are carried on in a dingy hole down cellar, which Tyndall denominated "the den." He is a single man of forty, with a scanty strip of forehead, and big, straight, prominent nose—the most restless, nervous creature I ever set eyes on. We stayed but a few minutes, and nothing was said of anything but the book, and the publication of books.

The work here referred to was Heat as a Mode of Motion, at that time in the hands of the printers in London.

Another letter written from Cambridge during the same visit, when he was attending the meeting of the British Association, describes Tyndall's manner as a lecturer:

Last night there was an address by Tyndall before the association in the lecture room; subject, water in its several conditions. It was altogether the most brilliant affair of the kind I have ever seen. The new philosophy of forces