In the course of the same year (1849) I sent a model of my Trunnion turn-table telescope for exhibition at a lecture at the Royal Institution, given by my old friend Edward Cowper. In the model I had placed a neat little figure of the observer, but the head had unfortunately been broken off during its carriage to London. Mrs. Nasmyth had made the wearing apparel; but Edward Cowper wrote to her, before the lecture, that he had put "Sir Fireside Brick" all to rights in respect of his garb. His letter after the lecture was quite characteristic.

"The lecture," he said, "went off very well last night. All the models performed their duty, and were duly applauded for doing so. My new equatorial was approved of by astronomers and by instrument-makers. The last gun I fired was a howitzer, but mounted swivel-gun fashion; on a sort of revolving platform, or something like a turn-table proper -- the gunner at the side of the carriage. Do you know anything of the kind? Bang! Invented by one Nasmyth. Bang! The observer is sitting at ease; the stars are brought down to you instead of your creeping up a scaffolding after the stars. Well, the folks came to the table after the lecture, and 'The Nasmyth Telescope' kept banging away for a quarter of an hour, and was admired by everybody. The loss of light was not much insisted on, but it was said that you ran the risk of error of form in three surfaces instead of two. I see that Sir J. South states that Lord Rosse would increase the light of his telescope from five to seven by adopting Herschel's plan

"De La Rue was quite delighted. He said, 'Well, I congratulate you on a most splendid lecture -- I cannot call it anything else.' My father, who takes very little interest in these things, said, 'Well, Edward has made me understand more about telescopes than I ever did in my life.' The theatre was full, gallery and all. They were very attentive, and I never felt more comfortable in a lecture. I am happy to say that, having administered a dose of cement to Mrs. Nasmyth's friend, Sir Fireside Brick of Green Lanes, he is now in a convalescent state. The lecture is to be repeated in another fortnight. With many thanks for your kind assistance, yours very sincerely,

"EDWARD COWPER."

In the course of my astronomical inquiries I had occasion to consider the causes of the sun's light. I observed the remarkable phenomena of the variable and some times transitory brightness of the stars. In connection with geology, there was the evidence of an arctic or glacial climate in regions where such cannot now naturally exist ;thus giving evidence of the existence of a condition of climate, for the explanation of which we look in vain for any at present known cause. I wrote a paper on the subject, which I sent to the Astronomical Society. It was read in May 1851. In that paper I wrote as follows:

"A course of observations on the solar spots, and on the remarkable features which from time to time appear on the sun's surface, which I have examined with considerable assiduity for several years, had in the first place led me to entertain the following conclusion : namely, that whatever be the nature of solar light, its main source appears to result from an action induced on the exterior surface of solar sphere,-- a conclusion in which I doubt not all who have attentively pursued observations on the structure of the sun's surface will agree.

"Impressed with the correctness of this conclusion, I was led to consider whether we might not reasonably consider the true source of the latent element of light to reside, not in the solar orb, but in space itself; and that the grand function and duty of the sun was to act as an agent for bringing forth into vivid existence its due portion of the illuminating or luciferous element, which element I suppose to be diffused throughout the boundless regions of space, and which in that case must be exhaustless.

Assuming, therefore, that the sun's light is the result of some peculiar action by which it brings forth into visible existence the element of light, which I conceive to be latent in, and diffused throughout space, we have but to imagine the existence of a very probable condition, namely, the unequal diffusion of this light-yielding element, to catch a glimpse of a reason why our sun may, in common with his solar brotherhood, in some portions of his vast stellar orbit, have passed, and may yet have to pass, through regions of space, in which the light-yielding element may either abound or be deficient, and so cause