1.821.] Philosophical Transactions for 1821, Part I. 231 



inches in width, this form being susceptible of the greatest 



directive force. . ,, . fi . 



« That the best mode of tempering a compass needle is, first, 

 to harden it at a red heat, and then to soften it from the middle 

 to about an inch from each extremity by exposing it to a heat 

 sufficient to cause the blue colour which arises again to dis- 



aP E 6 That in the same plate of steel, of the size of a few square 

 inches only, portions are found varying considerably in then- 

 capability of receiving magnetism, though not apparently differ- 

 ing: in any other respect. 



<< That polishing the needle has no effects on its magnetism. 



" That the best mode of communicating magnetism to a nee- 

 dle appears to be by placing it in the magnetic meridian joining 

 the opposite poles of a pair of bar magnets (the magnets being m 

 the same line), and laying the magnets so joined flat upon the 

 needle with their poles upon its centre ; then having elevated the 

 distant extremities of the magnets, so that they may form an 

 ano-le of about two or three degrees with the needle, they are to 

 be S drawn from the centre of the needle to the extremities care- 

 fully preserving the same distance from the needle, lhe opera- 

 tion is to be repeated 10 or 12 times on each surface. 



« That in needles from five to eight inches in length, their 

 weights being equal, the directive forces are nearly as the 



"That the directive force does not depend upon extent of sur- 

 face, but in needles of nearly the same length and form is as 



the mass. ■ .j. + i 



" That the deviation of a compass needle occasioned by tne 

 attraction of soft iron, depends, as Mr. Barlow has advanced, on 

 extent of surface, and is wholly independent of the mass, except 

 a certain thickness of the iron, amounting to about two-tenths ot 

 an inch, which is requisite for the complete developement ot its 



attractive energy* t 



XI. Notice respecting a Volcanic Appearance in the Moon. In 

 a Letter addressed to the President, by Capt. Henry Kater, 



FRS. ' , . ,, 



XII. A further Account of Fossil Bones discovered a» governs 

 inclosed in \he Limestone Rocks at Plymouth, By Joseph \Vhid- 

 bey, Esq. In a Letter addressed to Sir Everard Home, Bart. 



VPRS. . 3 „ , 



XIII. On the Aeriform Compounds of Charcoal and Hydrogen, 

 toith an Account of some additional Experiments on the sases 

 from Oil and Coal. By William Henry, MD. FRS. 



This very excellent paper is given at length in the present 

 number of the Annals. 



