LENZ OX ELECTRO-AJAGXETISM. 611 



would necessarily increase the force of the electrical current, I there- 

 fore made the following experiment. I wound round the armature ten 

 convolutions of copper wire bespun with silk, and the conducting wires 

 were connected with the ends of this spiral only by a single twist of the 

 ivires ; the result of the four readings off amounted to 36°"8 ; upon this 

 the same connection was made by twisting the ends of the wires ten 

 times round one another as tightly as possible ; the deviation amounted 

 again to S6°"8 ; I finally pressed the last connection as tightly as pos- 

 sible together with a pair of pinchers, so that they were very much 

 flattened ; the deviation was 36°*75. We may therefore consider the 

 connection made by tightly twisting the wires ten times round one 

 another as quite sufficient, and this was therefore made use of in all the 

 subsequent experiments. The places where the connection was made 

 were then wound round with silk stuff in order to secure them from 

 reciprocal contact. 



The second preparatory experiment I made in order to see whether, 

 when I advanced the electromotive spiral on the armature more to the 

 north limb or to the south limb of the magnet, it had any influence on 

 the electric current. For this purpose I obtained with two convolu- 

 tions the following results : 

 The convolutions advanced till in contact with the north limb 



of the magnet, gave a deviation = 5°'55 



The convolutions advanced until in contact with the south limb 



of the magnet, gave a deviation = S^'SS 



The convolutions advanced to the middle of both limbs gave a 



deviation = 5°"60 



therefore this influence also of the different positions of the spirals on 

 the armature is imperceptible : from this time I always placed them so 

 that the spirals occupied the middle of the armature. 



I thirdly determined, before I proceeded to the proposed experiments, 

 the thickness of the copper wires employed ; I weighed two feet of 

 each having wound off the silk, by which I obtained the propoitions of 

 their diameter on which it principally depended ; but in order to ob- 

 tain also their absolute thickness, I measured the thickest by means of 

 a micrometrical contrivance : I obtained the following results, in which 

 I have designated the vires, beginning with the thinnest, Nos. 1, 2, 3, 

 and 4. 



grains inch. 



2 feet of wire No. 1 weighed = 23-3 ; absolute thickness = 0*023 



2 No. 2 = 27-4. ; = 0-025 



(wire of the multiplier) 



2 No. 3 weighed = 83*9 ; absolute thickness = 0'044' 



2 No. 4 = 166-1 ; = 0-061 



All the four kinds of wires were well covered with silk, so that no 

 Vol. I.— Part IV. 2t 



