604 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



If the apparatus could be attached to a storage battery on which 

 there were no other loads, it would be comparatively easy to get 

 closer regulation by using a narrower range of current variation. 

 The battery used in these experiments is liable to have other loads 

 thrown on at any time. The curves (Fig. 2) show the variations 

 plotted from the tables. 



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20 



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G 8 10 



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Next the existence of a vertical temperature gradient was examined. 

 Readings on thermometer were made at different levels and no sure 

 difference of temperature was observable when the space inside heater 

 is empty. When masses of metal or other obstructions were placed 

 inside, slight differences amounting to one thousandth of a degree 

 were observed. In experiments like this all the windows in the 

 apparatus must be covered as radiation causes noticeable differences 

 in temperature. 



The platinum thermometer led to another important discovery. 

 Even after the automatic controlling apparatus becomes steady it 

 was found that the temperature of the air inside the heater continues 

 to rise. This is due to the fact that altogether the wall of the heater 

 box is about 1.8 cm. thick and while the mean temperature of the 

 mercury in the wall does not vary, the temperature of the inner part 

 and the wall adjacent to it is rising while that of the outer part is fall- 

 ing. This rise may amount to more than .1° and it is a matter of 

 an hour or so before it disappears. This time has been shortened by 

 placing a small flat heating coil of fine GS wire along the inner wall 

 inside. A small current sent through this helps to establish equi- 



