and on Variations in the Fixed Lanes of the Solar Spectrum. 343 



But Mr. Tomlinson knows better than this. He sees on page 

 99 of the Appendix of the book he has quoted, and in the fourth 

 line from the top of the page, that the experiments he refers to, 

 and the paragraphs he quotes, were published, not in 1844, as 

 he would have his readers suppose, but in 1837, in the Journal 

 of the Franklin Institute of Philadelphia for June, July, August, 

 and September of that year. They are not later contradictions 

 of the true explanation given in 1840, but the earlier steps by 

 which that conclusion was gradually reached. They were pub- 

 lished, not four years subsequently, but three years previously to 

 the correct explanation. 



I have made no new experiments on these camphor-motions 

 since 1840, knowing that the explanation I then gave is the true 

 and final one. 



In 1844 I collected together and reprinted several of the papers 

 I had published during the preceding ten years in English and 

 American journals, those in the Philosophical Magazine among 

 the rest. 



Having been drawn into this camphor-controversy very need- 

 lessly and very reluctantly, you, Gentlemen, will perhaps accord 

 me the privilege of the space of a few additional lines to ask the 

 attention of your readers to another topic. 



In the same Number of the Philosophical Magazine in which 

 Mr. Tomlinson's original communication occurs, November 1862, 

 p. 407, there is a brief account of the recent discoveries of Dr. A. 

 Weiss on the lines of the solar spectrum, to the effect that he 

 had observed in Greece, during the preceding year, the Fraun- 

 hofer lines at sunrise and sunset, and had remarked their increase 

 of number and their condensation. Dr. Weiss points out the 

 advantages of the Ionian Islands for these observations, remark- 

 ing that the dense layers of vapour observed almost every day on 

 the coasts of Africa and America, there scarcely disturb the 

 observer. He also refers to his previous publication on changes 

 of the breadth of these lines at sunset, especially in the red and 

 yellow rays, and to the explanation he has given of their disloca- 

 tion by lateral absorption, Phil. Mag. July 1861, p. 80. With 

 that explanation I am not at present interested. 



But I wish to relieve the atmosphere of America from the 

 reproach here unfairly put upon it, since it was in it, and by 

 myself, that the fact in question was many years ago remarked. 

 If your readers will turn to the Philosophical Magazine for May 

 1843, p. 361, they will find the following paragraph, in con- 

 nexion with the photographic depicting of Fraunhofer's lines : — 



" Before proceeding to the description of the mode which is to 

 be followed, and of the characters of the lines themselves, I can- 



2 A2 



