in proportion to its length. 333 



joining spirals of the thread wound on the wire, there is sufficient 

 room for another spiral of thread, and on a great part of the 

 wire there is space enough to admit three or four threads. I 

 adopted this mode of covering the wire in order to save time. 

 With the same view, I aiTanged our machine for winding thread 

 on wii'e so that by one and the same operation I covered the 

 wire with thread and wound the wire on the coil. I fear that 

 in many parts of the coil the bare or uncovered part of one wire 

 is in contact with some parts of the adjoining wires. Each layer 

 of spirals is brushed over with a hot solution of gutta percha 

 dissolved in rosin oil. The solution is so thick, that when cool 

 it takes the form of a paste. Each layer of spirals is insulated 

 from those of the layer above and below it by paper saturated with 

 the solution of gutta percha, in the manner described in the paper 

 which I read at the Dublin Meeting of the British Association 

 in 1857, and which was published in the Philosophical Magazine 

 for the following November. I have in one instance seen sparks 

 passing through the three thicknesses of paper, by which the 

 spirals in one layer are insulated from those of the one above 

 it. Hence the insulation of each layer of spirals from those above 

 and below it is defective. 



In trying the two parts of the coil which were first made, I 

 observed, as often as sparks passed between the terminals of the 

 coil, a great number of very minute sparks on the outside of one 

 of the two parts. This made me suspect that these sparks were 

 passing from some spirals to the adjoining ones. "When I had 

 finished the third part of the coil, I abstained from brushing 

 over the outside spirals with the solution of gutta percha, in order 

 to see whether sparks would pass from one spiral to another. 

 As soon as the battery was connected with the primary coil by 

 means of our mercurial contact-breaker, sparks passed from the 

 bare parts of several wires to the contiguous ones. When any 

 part was brushed over with the gutta-percha solution, the sparks 

 ceased there, but became more numerous in some other part. 



This coil, though only 5 inches long, has, notwithstanding 

 all its defects, given sparks 4^ inches in length with three cells 

 of the Maynooth battery, each 4 inches square. I have not 

 seen an account of any coil which with so small a battery has 

 given sparks so long in proportion to the length of the coil. 

 On account of the imperfect insulation of the secondary coil, I 

 am afraid to use a more powerful battery. 



T intend to make a new primary coil about 36 inches long, 

 and twelve small secondary coils, each about 2 inches in length. 

 From this coil I expect to get, with a small battery, sparks 20 

 or 24 inches long. 



I have made several interesting experiments on -the variou» 



