TRANSACTIONS OF SECTION A. 555 



in the insulated ij-tute, and with an uninsulated (j-tube filled with sulphuric 

 pumice between the bellows and the insulated tube, so that the air entering it ia 

 artificially dried. With this arrangement the insulated y-tube was negatively 

 electrified by the blowing of the air through it ; but this electrification may have 

 been due to the negative electrification of the dry entering air to be expected from 

 the result of our first experiment. We intend to repeat the experiment with 

 artificially dried a7id dis-electrified air blown through the u"**^^® containing 

 pumice moistened with water. 



2. Preliminary Experiments for comparing the Discharge of a Ley den Jar 

 through different Branches of a Divided Channel. By Lord Kelvin, 

 P.B.S., and Alex. Galt, B.Sc, F.R.S.E. 



In these experiments the metallic part of the discharge channel was divided 

 between two lines of conducting metal, each consisting in part of a test-wire, the 

 other parts of the two lines being wires of different shape, material, and neighbour- 

 hood, of which the qualities in respect to facility of discharge through them are to 

 be compared. 



The two test-wires were, as nearly as we have been hitherto able to get them, 

 equal and similar, and similarly mounted. Each test-wire was 51 cm. of platinum 

 wire of "006 cm. diameter and 12 ohms resistance, stretched straight between two metal 

 terminals at the ends of a glass tube. One end of the platinum wire was soldered 

 to a stiff solid brass mounting ; the other was fixed to a fine spring carrying a light 

 arm for multiplying the motion. The testing effect was the heat developed in the 

 test-wire by the discharge, as shown by its elongation, the amount of which was 

 judged from a curve traced, by the end of the multiplying arm, on sooted paper 

 carried by a moving cylinder. Two of Lord Kelvin's vertical electrostatic volt- 

 meters, suitable respectively for voltages of about 10,000 and 1,500, were kept 

 constantly with their cases connected with the outer coatings of the leyden, and 

 their insulated plates with the inside coatings of the leyden. 



I. In the experiments hitherto made the two wires to be tested have generally 

 been of the same length. When they were of the same material, but of different 

 diameters, the testing elongation showed, as was to be expected, that the test-wire 

 in the branch containing the thicker wire was more heated than the test-wire in 

 the other branch. In a continuation of the experiments we hope to compare 

 hollow and tubular wires of the same external diameter, and same length and same 

 material. 



II. With wires of different non-magnetic material — for example, copper and 

 platinoid — of the same length, but of very different diameters, so as to have the 

 same resistances, the testing elongations were very nearly equal. 



III. In one series of experiments the tested conductors were two bare copper 

 wires, each "16 cm. diameter, 9 metres long, and resistance "085 ohm, which, it will 

 be observed, is very small in comparison with the 12 ohms in each of the platinum 

 test- wires. One of the copper wires was coiled in a uniform helix of forty turns on 

 a glass tube of 7 cm. diameter. The length of the helix was 35 cm., and the distance 

 from centre to centre of neighbouring turns therefore f cm. The middle of the 

 other copper wire was hung by silk thread from the ceiling, and the two halves 

 passed down through the air to the points of junction in the circuit. The elonga- 

 tion of the test-wire in this channel was more than twice as much as that of the 

 test-wire in the channel, of which the helix was part. 



IV. One hundred and seventy-one varnished pieces of straight soft iron wire 

 were placed within the glass tube, which was as many as it could take. This made 

 the testing elongation ten times as great in the other channel. 



V. The last comparison which we have made has been between iron wire and 

 platinoid wire conductors. The length of each was 5025 cm. The diameter of 

 the iron wire was •0.34 cm., and its resistance 6"83 ohms. The diameter of the 

 platinoid wire was "058 cm., and its resistance 6"82 ohms. Each of these wires was 

 supported by a silk thread from the ceiling, attached to its middle (as in III. and IV. 



