204- Mr. Wheatstone on the Velocity of Electricity. 



half fathoms of limestone and ten fathoms and a half of sand- 

 stone ; and at Eppleton only nine and a half fathoms of lime- 

 stone and twenty-one fathoms of soft sandstone. The Ele- 

 more Pits are one mile south-west of the Hetton Pits, and the 

 Eppleton about one mile north-east of the Hetton Pits." In 

 this part of the district the dip of the coal beds is towards the 

 east, at the rate of one yard in twenty-two ; but along the coast 

 of Northumberland, and as far south as Manor Walls End*, 

 at the mouth of the Tyne, they rise rapidly to the east, as well 

 as more gently towards the west. On the other hand the coal- 

 measures south of the river Wear continue to dip regularly to 

 the eastward. Even at Hetton the high main coal had not re- 

 covered the good quality it was formerly known to possess on 

 the Tyne ; but the low main, a very inferior coal, from being 

 brittle and breaking into small fragments before reaching the 

 London market, is at Hetton and other Wear water collieries 

 a coal of very superior quality. In all these mines the low 

 main of the Tyne is called the Hutton seam. See section of 

 Byker St. Anthon's Colliery, Geological Transactions, first 

 series, vol. iv. pp. 41, 42. 



[To be continued.] 



XXXIX. Remarks on one of Mr. Talbot's proposed Philoso- 

 phical Experiments. By C. Wheatstone, Esq. 



To Sir David Brewster. 

 Dear Sir, 



TN the last Number of the Philosophical Magazine is in- 

 ■*■ serted an article, entitled " Proposed Philosophical Expe- 

 riments, by H. F. Talbot, Esq. M.P. F.R.S." Upon a part of 

 this communication, headed " On the Velocity of Electricity," 

 I feel it necessary to make the following observations. 



My experiments were not made solely with a view to deter- 

 mine the velocity of the electric spark passing through air as 

 Mr. Talbot has inferred, but, from the first, were intended to 

 extend to the passage of electricity through solid conductors. 

 In fact, the very first experiment of the kind which I made, and 

 which was shown to the members of the Royal Institution on 

 the evening my investigations on this subject were first made 

 public by my friend Dr. Faraday, was one by which I endea- 

 voured to show the deviation from a vertical line of two sparks 

 simultaneously visible at the opposite ends of a metallic con- 

 ductor. Beyond this, I have for several months past commu- 

 nicated very generally to my scientific acquaintance the de- 



* Almost all coals with us are now designated Walls End, whatever 

 seams may produce them. 



