had been asked to present the subject of electricity in the household. I replied to the programme committee that that was too large a

her was unfavourable to outdoor sports, and that February usually found them acclimated to vi

girls and boys. Most of them had left school-many of them be

g.

for our experiments. I propose to show that we convert electricity into heat by offering resistance to its flow. Experience teaches us that resistance to motion always produces heat. At Niagara Falls thousands of tons of water descend at the

Niagara Falls. The resistance to their motion, which our atmosphere offers, heats them white hot, melts

at the rate of twenty miles an hour. The energy of this moving mass depends upon both its weight and its velocity, and when its motion is

made red hot by poundin

al at Munich, that the resistance which the iron offered to th

e pound of water (one pint) one degree. This is called the British thermal unit. The spile driver, weigh

g.

uit by stretching between a and b 8 feet of No. 24 iron wire. (This wire is about the thickness of a common pin.) The iron wire offers resistance to the flow of the electric current

ammeter at first indicates 20 or 30 amperes, but in a second drops to 8 amperes, and remains there a second until the wire melts an

g.

/(14 ohms)

8 amperes

= one ho

the wire in a second, and the heat produced was a little les

ed 1 foot =

s per second =

. (British thermal unit) = heat require

1 amper

s = 1 ho

t not more than eight amperes of electricity should pass, t

d than when hot. Indeed eight feet of No. 24 iron wire offers about one and one third ohms resistan

vel more coal into the furnace. The heat of the burning coal melts the wire, but it does it only after several changes. First, it is converted into mechanical energy in the steam-engine with great loss-about nine tenths being lost. Second, it is converted into electrical energy by the dynamo, with some loss, and, third, it is conducted to the iron wire and c

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ank of water, T. While things are in this condition I move the crank which operates the pump with perfect ease. Now while still turning the crank I pick up the tube a and drop its free end into the water tank. I cannot now conceal the fact, even if I were disposed to do so, that I must work hard to keep the pump going. The pump itself tells you by its laboured sound that it is working hard, and the stream of water which issues from the pipe b tells how much work I am performing

ittle resistance, except that stretched between the binding posts a and b. This is a piece of fine German silver wire. While the switch is open I turn the crank of the dy

or decreases according to whether I rotate the armature faster or slower. Now I will attempt to keep the machine revolving at a constant rate while I close the switch S, and

The lad now takes my place at turning the machine and finds it easy when the switch is open, but I actually over

that each person should get a realizing sense of this fact, first by doing the work himself, and second by going home and reflecting upon this hint. When the switch is closed three amperes of electricity pass arou

d delivered to them the second key to the Electrical Sho

e flow of the electric current. The first key is the elec

t I had warned them before the lecture that they must work, so now each