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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1871 Excerpt:...had occupied 18 months in making and cost 350, and only showed 5 lines in the D group, but several persons had seen 13 lines with this spectroscope, proving its definition perfect. In fact, it saved the enormous waste of time caused by adjusting each prism to the minimum deviation for each ray, as Kirchhoff and Bunsen took the trouble to do between each observation. Dr. Huggins: The instrument does all that can be required, and would not be improved if mathematically perfect. Such a spectroscope as this must alter from day to day, and could not be used for the absolute determination of wave lengths. Its proper use is, as an instrument of comparison. Professor Pritchard: It appears to me to be an immense advance on the usual construction, and is exceedingly ingenious. Dr. Huggins: Certainly it is a great advance on all where the prisms do not move. I have not seen Elliott's instrument with a spring, but think this must be better. The President: I suppose it is very costly. What would a dozen come to? Mr. Browning: I should be very sorry to take an order for a dozen. Lieut. Brown enquired whether the prisms were all of the same glass? Mr. Browning: Yes. They are Chance's dense glass, but not his double dense. The latter glass has so much lead in it that it becomes discoloured from the sulphur always about, such as the neighbourhood of india-rubber bands, &c. Note on Father Secchi's Letter to the Academy of Sciences, April 25, 1870": by Mr. Seabrooke. The author having been allowed the use of Mr. Lockyer's telescope and spectroscope for some time past, thinks it right to add his testimony to Mr. Lockyer's as to the correctness of the latter in the matter discussed in Father Secchi's communication. He (P. S.) therein states that the velocity of rotatio...