130 Mr. J. Murray on the Deviation of the Magnetic Needle. 



XXIII. Experiments on the Deviation of the Magnet icNecdle,ias 

 effected by Caloric, fyc. By John Murray, Esq. F.8.A. 

 F.L.S. F.H.S. Member of the Geological and Wernerian So- 

 cieties, S)-c. Sj-c. 

 To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



I TRUST the following detail of experiments on the devia- 

 tion of the magnetic needle as effected by caloric, &c. 

 will prove not uninteresting. They at once corroborate and 

 extend some remarks of mine you did me the honour to intro- 

 duce in a former Number of the Philosophical Magazine and 

 Journal. 



It may be only necessary to premise, that for the subsequent 

 experiments I used a very delicate magnetic needle, about six 

 inches long, the point on which it moved entering an agate 

 cap. So extremely mobile was the magnetic bar, that simple 

 pressure by the finger on the sealing-wax was sufficient excite- 

 ment, and a ribbon of silk once drawn over the glass tube 

 quite enough for the vitreous or positive electricity. 



In the comparison of the phenomena, the heated zinc 

 plate will be found to accord with the excited glass, and the 

 silver plate with the sealing-wax. The flames of a wax taper 

 and spirit lamp are analogous, but the aphlogistic platinum- 

 wire peculiar. 



The north pole, in these experiments, moved usually about 

 the octant of a circle eastward of north, and the south pole 

 about the same number of degrees (45°) westward of south. 



1. Excited Glass. 

 Posited east of north, repelled : and on removal, the needle 



moved eastward, and returned to its station. 

 On the west of north, attracted : moved eastward. 

 On the east of south, repelled. : moved westward. 

 On the west of south, attracted : ditto. 



2. Excited Sealing-Wax. 



On the east of north, attracted : moved eastward. 

 On the west of north, ditto : ditto. 



On the east of south, ditto : moved westward. 

 On the west of south, ditto : ditto. 



3. Iiiflamed Wax Taper. 



On the east of north, attracted : moved eastward. 

 On the west of north, ditto : ditto. 



On the east of south, ditto : moved westward. 

 On the west of south, repelled .• ditto. 



. 4. Spirit 



