92 



source of gravity, and other centra] forces ; and it is not impossible 



but that the relations of this medium to the particles of common 

 matter may admit of considerable modification or change, and which 

 may be the source of that peculiar power we find displayed in those 

 bodies we consider as being magnetic and call magnets. It has been 

 occasionally supposed that in the reciprocal force between magnets 

 and iron there is a peculiar agency in operation, the law of which is 

 disturbed by the new forces of induction liable to ensue in changing 

 the distances. The author ho^vever is of opinion that such a notion 

 is inconsistent with the course of nature; it is induction which con- 

 stitutes magnetic action, there is no other form of action; when in- 

 duction is not present there is in fact no action; we must hence 

 lock to these very changes for an explanation of variable magnetic 

 force. 



10. Researches into the Identity of the Existences or Forces, 

 Light; Heat, Electricity and Magnetism." By John Goodman, ^NI.D. 

 Communicated by Thomas Bell, Esq., Sec. R.S. &c. Received 

 March 7, 1851. 



In this communication the author describes the effects that were 

 produced on a moderately sensitive galvanometer by exposure to 

 the sun's rays, and which were observed by him during a period of 

 four months, commencing on the 1-ith of November, 1850. The 

 instrument is described as consisting of forty-six turns of covered 

 copper wire, ,Tjth of an inch in diameter. The hehx is blackened with 

 ink at its southern extremity, and has a single magnetized sewing- 

 needle suspended by about sixteen inches of silken fibre in its centre. 

 The dial, which is of card-board, and divided into the usual number 

 of degrees, rests upon the upper surface of the helix, and shades it 

 from the ordinary light or sun's rays, except at its extremities, and 

 occasionally some portions of the lower bundle of wires ; and when 

 the sun is very low the rays may be seen also to illumine to some 

 extent the surface of the upper bundle. The indicator is formed of 

 a slender filament of light wood in the usual manner, and the whole 

 is enclosed in a glass shade. This instrument was placed for ex- 

 periment in a window having a southern aspect; and whilst the sun 

 was strongly shining upon it, it was frequently observed that there 

 could not be obtained, either on account of vibrations or the erro- 

 neous condition of the instrument, any true indications. On shading 

 the instrument from the sun's rays by a screen, the vibrations ceased, 

 and the needle again adjusted itself north and south. 



On removing the screen the needle began again to vibrate, and 

 was soon discovered to become stationary at some distance from 

 zero, indicating the transmission of a current in the helix. This de- 

 flection of the needle was soon found to be always, under the same 

 circumstances, in the same direction, and to give indications of a 

 current corresponding to the brightness of the sun. 



This action appeared to depend upon the incidence of the sun's 

 rays upon the south extremity, and some of the lower or upper 

 bundle of wires only of the helix ; for when they began to illumine 



