On the Coal and Stone Strata of Durham. S63 



talists on the continent. I liave since tried the experiment, and 

 find it succeeds perfectly, but requires a more extensive series to 

 overcome the increased friction. 



An effect very nearly resonbling the action of the beam of a 

 steam-engine may be produced by placing the needle in a hori- 

 zontal instead of a vertical position. For this purpose it should 

 be constructed in the same manner as an ordinary scale-beam j 

 having equal arms terminated by gilt balls, and its point of sus- 

 pension above its centre of gravity. If a needle of this kind be 

 insulated, and placed with one of its balls a few inches above 

 the positive extremity of a powerful column, whilst the opposite 

 ball is similarly situated with respect to the negative extremity, 

 it will, when once put into a state of oscillation, continue to move 

 with considerable regularity, and with a momentum which ren- 

 ders it probable that, by the application of a proper mechanical 

 arrangement, a tolerably regular source of rotatory motion would 

 be obtained. 



I have now completed a series of columns comprising up- 

 wards of .50,000 groups of a peculiar and powerful arrangement, 

 but have not as yet combined them so as to institute any accurate 

 experiments on their effects ; but I trust it will not be long ere 

 I have leisure to accomplish this object. 



London, May 1, 1815. G. J. SiNGER. 



LXV. On the Coal and Stone Strata nf Durham. By 

 Nat. John Winch, Esq. of Newcastle, 



To Mr. Tilloch. 



SiVi, — If your correspondent who writes under the ■signature 

 of " A Constant Ileader," in the Philosophical Magazine, has 

 access to the papers of the Geological Society of London, I beg 

 icave to recommend him to inspect the numerous sections of 

 collieries situated in this vicinity, which are deposited in the li- 

 brary of that Institute. By taking this trouble, he vyill soon per- 

 ceive that strata of stone and coal vary not only in thickness, 

 but are sometimes replaced by beds of different descriptions at 

 places by no means distant from each other ; and of course that 

 a single 'section, such as that adopted by Mr. Forster, can convey 

 but a very inadequate idea of the straLification of this part of the 

 kingdom. But should his residence be out of town, the fol- 

 lowing information relative to the Newcastle grindstone bed 

 may prove acceptable to him. Qn Gateshead Fe 1 and Wick- 

 ham Banks (see the Map of Durham) this stratum is 1 1 fathoms 

 thicl;, and lies 38 fathom's above the High Main Coalj it is also 



met 



