mann] THE PHYSICS OF INDUSTRY 15 



discussion, the class decided that it would like to construct 

 thermometers, in order to be able to make measurements of 

 temperature and be able to answer their own questions. 



This piece of work lasted several weeks, but at the end of that 

 time each pupil was the proudand happy possessor of a thermom- 

 eter of his own manufacture. During the process of making 

 they had learned something of glass blowing, and had begun to 

 clarify their notions of temperature, boiling point, and melting 

 point. They had reasoned out the fact that thermometer 

 scales were arbitrarily selected for convenience: they had found 

 that ice and boiling water remain at constant temperature through 

 change of state, and had seen that heat is required to produce 

 melting and evaporation. They were, however, unable to grasp 

 the idea of heat quantity as measured in B. T. U.; for thtm a 

 quantity of heat was simply so many degrees on the thermcmeter. 



In filling the thermometers mercury, water, alcohol, and air 

 were used for thermometric substances, and their various ad- 

 vantages and disadvantages discussed. They reasoned out the 

 conditions that must be fulfilled in making thermometers that 

 should be very sensitive through a small range, or good for low 

 temperatures only, or for high temperatures only, or for a large 

 range of temperatures. 



When all the instruments were done, they were hung on the 

 wall together and readings taken for several days. Of course 

 the readings at a given time differed among themselves by 10 

 or 15 degrees. Although the question as to how to find the 

 right temperature from all the thermometers which gave such 

 different readings at first showed that each child thought his own 

 was correct, one or two bright ones eventually suggested that 

 taking the average of all the readings would give the most 

 probable value. This was done, and the average agreed very 

 closely with the reading of a standard thermometer. 



When the thermometers were completed, the manufacture of a 

 hot-water heater was taken up. This was made from glass 

 tubing and corks, each member of the class making his own 

 design, generally copied from the one at home. It is probably 

 not necessary to enumerate the important physical ideas that 

 are involved in this device. Nothing was ever said to them about 

 laws, they simply observed and absorbed knowledge of how the 

 water acted under the conditions thev created. 



