192 Sir Frederick Bramwell [April 18, 



5,000,000 amperes of quantity by 1 volt of pressure ; but whatever 

 the form may be, there are still 5,000,000 watts. 



Now let us take another illustration, a monetary one. Suppose I 

 wish to send live pounds of money by post ; it would obviously be 

 best that I should send it in the form of a 5/. note. It weighs less 

 than five sovereigns, and takes up less room. Take this as an illus- 

 tration of the greatest " pressure " and the least " quautity." Suppose, 

 however, I want to give 100 Sunday school children each a shilling, I 

 do not want either a 51. note, or even five sovereigns ; I want 100 

 shillings. I should have then a comparatively great weight, which it 

 would not be so convenient to send by post, but which is, however, 

 in a suitable form for my purpose of distribution to the children. 

 This is my five pounds sterling in the form illustrating large 

 quantity and low pressure. 



Similarly in the case of electricity. Depending upon the con- 

 struction of the dynamo, and upon its velocity of revolution, you 

 can produce your electricity either in the form of high voltage and of 

 small quantity, or, if the construction is varied, of low voltage and 

 of large quantity — either the 5/. note or the shillings. But if you 

 produce it in the condition of large quantity and of low pressure, 

 and you desire to transmit it to the smith for him to use it in welding 

 machines, you will find that form of current to be very inconvenient, 

 because it clearly involves the employment of conductors so amjDle 

 in sectional area as to admit of all this large quantity being brought 

 through them to the iron, to heat it up to the welding point, without 

 the waste of electrical energy due to useless heating up of the con- 

 ductors themselves. The conductors must therefore be very large, 

 and of yevj excellent conducting material. Therefore it is desirable 

 to produce the electricity in the 61. note form in the first instance, 

 and convert it into the shilling form, or it may be even into the 

 form of farthings, after it has been transported to the very machine 

 in which it is to be used. 



Now how is this change to be made '? Who is to be our money 

 changer? Who is to change the electricity of small quantity and of 

 high pressure into that of large quantity and low pressure ? Some 

 half century ago Euhmkortf invented the coil by which, as you have 

 all seen, the low potential or j)ressure of a few cells of a battery, 

 incapable of making an appreciable sjjark, is translated into small 

 quantity and large voltage, capable of leapiug through considerable 

 distances. We have before us here, at my right hand, a Ivuhmkorlf 

 coil, which contains 70 yards of primary wire, weighing 6 lbs. The 

 secondary coil is 8 miles in length, and weighs 1'2 lbs. The sec- 

 tional areas of these two wires are as 100 to 1. We have a battery 

 here of five cells. We will put it to work, in conjunction with the 

 <;oil, in the first instance sin)ply to give us a spark. You will see 

 now it has converted the low potential of the five cells into that 

 which is capable of leaping across a space of 1| iuclies, and you 

 can, with suitable arrangements, get results a great deal higher than 



