350 Prof. A. M. Mayer on the Effects of Magnetisation 



If these researches were executed for homogeneous rays, we 

 might obtain interesting information as to the constitution of 

 the sun's atmosphere. 



The author of the above paper seems to have been unaware 

 of the observations taken by Professor Roscoe in 1863 and com- 

 municated to the Royal Society (see Phil. Mag. vol. xxvii. p. 384), 

 Professor Roscoe has proved that the intensity of the chemically 

 active rays at the centre of the sun is greater than at the edge 

 of the disk. The absorption of the sun's atmosphere, according 

 to Professor Roscoe' s experiments, is not so large as that result- 

 ing from VogePs observations. Calling the intensity at the 

 centre of the solar disk 100, the mean of Roscoe' s observations 

 gives about 28 for the intensity at the edge, while Vogel gives 13. 

 The discrepancy may be partly accounted for by the rapid de- 

 crease in the intensity near the edge ; but it is likely that this is 

 not the full explanation of it. Vogel does not state whether he 

 used a refracting or a reflecting telescope. Suppose he used a 

 reflecting one, the mean wave-length of the rays the intensity 

 of which he measured would be smaller than that of the rays 

 measured by Roscoe, who used a refracting telescope; and if 

 this should be so, it will add another proof of the^fact that the 

 smaller the wave-length the greater is its absorption. — Arthur 

 Schuster, Ph.D. 



XLIIT. On the Effects of Magnetization in changing the Dimen- 

 sions of Iron, Steel, and Bismuth bars, and in increasing the 

 Interior Capacity of Hollow Iron Cylinders.— -Part I. By 

 Alfred M. Mayer, Ph.D., Professor of Physics in the Ste- 

 vens Institute of Technology, Hoboken, New Jersey, U.S.A.*. 



I PURPOSE giving, in a series of papers, the results of a 

 prolonged and careful research on the above subject." 



Introduction. — In 1842 Joule discovered that when a current 

 of electricity was passed through a helix which enclosed a bar of 

 iron, the latter, on its magnetization, suddenly elongated a mi- 

 nute fraction of its length. 



To present clearly Dr. Joule's experiments, we will give these 

 abstracts from the excellent paper which he published in the 

 Philosophical Magazine in 1847 : — 



" In order to ascertain how far my opinion as to the invari- 

 ability of the bulk of a bar of iron under magnetic influence was 

 well founded, I devised the following apparatus. Ten copper 



* Communicated by the Author, having been read before the National 

 Academy of Sciences in Cambridge, Massachusetts, November 22, 1872. 



