Mr. Stark on the Sand-pipes in the Chalk near Norwich, ^55 



Now, by (23. )j e is connected with Jc\ hence it follows that the 

 diminution of the intensity of the light, in traversing any me- 

 dium, depends on the thickness of the medium and the length 

 of the wave. 



I'his inference agrees with what we learn bj' experiment ; 

 therefore we may say that our formulae afford, so far, an ex- 

 planation of the cause of the absorption of light. The cause 

 subsists in the values of x given by the equation (13.). In all 

 media for which these values are, severally, partly real and 

 partly imaginary, absorption must take place. 



It is my intention to pursue this subject further in another 

 paper. 



I am, Gentlemen, yours, &c., 



John Tovey. 



Littlemoor, near Clitheroe, Nov. 4, 1839. 



LXIXi Observaiio7is on Mr. Lyell's Paper, entitled^ " On the 

 tuhidar Cavities Jblled with Gravel and. Sand, called Sand- 

 pipes, in the Chalk near Norxvich." By William Stark, 

 F.G.S. 



To the Editors of the Philosophical Magazine^ and Journal, 

 Dear Sirs, 



"VT'OUR Magazine of the present month contains a paper 

 -*- by Mr. Lyell on the " Sand-pipes in the chalk near 

 Norwich," upon which I beg to offer a few remarks. 



In the first place allow me to observe that the description 

 tvhich Mr. Lyell has given of the forms of the chalk pits and 

 sand-pipes in this neighbourhood is very accurate, and the 

 engravings by which it is illustrated are excellent representa- 

 tions of the originals. The hypothesis, however, that he ad- 

 vances relative to the origin of their formation, is, in my 

 opinion, far from being satisfactory. The order of arrange- 

 ment which he has adopted does not appear to me the most 

 suitable : nevertheless I will take it as it stands. 



He says, " For the distance of several inches, or even in 

 some places four or five feet from its junction with the sand- 

 pipes, the chalk at Eaton is moist and softened, and becomes 

 friable when dried, and is discoloured by containing a slight 

 mixture of fine sand, clay and iron, the same chalk being 

 quite pure, and perfectly soluble in acids at points more re- 

 mote from the pipes." 



This does not correspond with the result of my experi- 

 ments upon the same chalk, however remote from the sand- 

 pipes. I did not find it " quite pure"; it was not ^* perfectly 



