Royal Society, 499 



alone, nor without the formation of a complete electrical circuit. 

 But in these experiments hitherto the completion of the circuit 

 had not been attempted. During the course of the experiments 

 the circuit was established by means of a connecting wire between 

 the mercury cups, and the circuit was again and again completed, 

 and as frequently broken, without any deviation occurring in any 

 of the results, either during the progression, stationary condition, or 

 decline of the needle. 



That these phenomena were the result of the action of the sun's 

 rays upon the helix itself,was further shown, from the circumstance 

 that when the sun remained clouded for days together, there was no 

 deflection of the needle ; that when the helix was partly shaded by a 

 pillar, or the window-frame, the instrument indicated an amountof cur- 

 rent corresponding to the number of coils of wire illumined; and that 

 the illumination of the whole bundle of wires at the southern extremity 

 of the helix was necessary to produce the usual results, for when a 

 burning lens of high power was employed to condense the rays and 

 throw them in a focus upon one or two wires only, no deflection of 

 the needle was observed. It was also further shown that the action 

 of the rays upon the helix was attributable to that portion situate 

 chiefly at the southern extremity, for the whole instrument was in a 

 variety of ways and at different periods shaded from the solar rays ; 

 but its results were unaffected, unless the south end was obscured, 

 when the needle immediately declined; or the north end was illu- 

 mined when the deflections were lessened, .or the motion of the 

 needle took place in the opposite direction. 



A pile of red-hot burning embers held in the vicinity of one ex- 

 tremity of the helix caused a slight deflection of J°, and when held 

 at the opposite extremity, caused a deflection in the opposite di- 

 rection. 



The author states a remarkable circumstance, viz. that vibrations 

 and neutral action were observed during bright sunshine about the 

 11th of December, and again on the 23rd of January ; that previous 

 to the former period the deflections of the needle were to the left' 

 hand; between these two periods they were to the right-hand; and 

 after the latter period always to the left, after a given hour of the day. 

 During the early sun, however, they were to the right-hand, and as 

 the sun approached a given altitude, they were invariably to the 

 left-hand. Deflections observed during the summer season were 

 also to the left-hand \ but those of the early sun were not submitted 

 to the test. 



On testing the instrument with a voltaic pair, it was shown that 

 the current passed from south to north above the needle with the early 

 sun, or when the indicator deflected to the right-hand, and beneath 

 the needle with the rays which proceeded from a considerable eleva- 

 tion, or when the needle deflected to the left-hand. 



In conclusion, the author states that the results of these experi- 

 ments evince to his mind more than ever the unity of force-, and 

 that experimental evidence appears to justify the conclusion at 

 which he has long since arrived, that there is one, only, universal force 



