498 Royal Society, 



" Researches into the Identity of the Existences or Forces, Light, 

 Heat, Electricity and Magnetism." By John Goodman, M.D. 

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



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 Hth of November, 1850. The 

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

 copper wire, j^ih of an inch in diameter. The helix 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 

 the opposite extremity, either very slight indications, or a neutral 

 result, constant vibrations, or the movement of the needle some de- 

 grees in the opposite direction, were always observed. The maxi- 

 mum deflection, at any time attainable by the galvanometer, when 

 the sun was quite unclouded, was about 12°, generally only 10°. It 

 may be observed that in all these experiments the power of the rays 

 was probably somewhat diminished, by passing though the glass 

 pane of the window, and through the glass shade of the instrument 

 itself. 



In order to show that the effect was not thermo-electric action, 

 the extremities of the helix were removed from their mercury cups 

 and wrapped in paper, so as to exclude the mercurialized portion of 

 the copper from the action of the sun's rays ; but no alteration oc- 

 curred in the ordinary results of the experiments. There is, more- 

 over, the author considers, no evidence on record of any thermo- 

 electric action ensuing from the application of heat to copper wire 



