584 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



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to Calv."^ 



Jiero 



j^ir Spacer -: 



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sene 



The Energy Measurements. 



Before rejecting the bolometer method used in the preliminary meas- 

 urements of energy, a secouii bolometer of slightly different construction 

 was tried; but the lack of uniformity of resistance, already mentioned, 

 made its indications too uncertain for the present work. The radiant 

 intensity of the beam used in the later experiments was determined 

 by directing it upon the blackened face of a silver disc, weighing 

 4.80 grams, of 13.3 mm. diameter and of 3.58 mm. thickness, and by 



measuring its rate of 

 temperature rise as it 

 passed through the tem- 

 perature of its sur- 

 roundings. The disc 

 was obtained from 

 Messrs. Tiffany & Co. 

 and was said by them 

 to be 99.8 per cent 

 *toCalv. fine silver. Two holes 



were bored through 

 parallel diameters of 

 the disc, one-fourth of 

 the thickness of the disc 

 ThinBoard from either face. Two 

 -- Box- iron-constantan thermo- 



junctions, made by sold- 

 ering 0.1 mm. wires of 

 the two metals, were 

 drawn through the 

 holes into the centre of 

 the disc. To insulate 

 the wires from the disc, 

 fine drawn glass tubes 

 were slipped over them 

 and thrust into the 

 holes, leaving less than 

 2 mm. bare wire on 

 either side of the junctions. The wires were sealed into the tubes, and 

 the tubes into the disc by solid shellac. The tubes projected 15 mm. or 

 more from the disc and were bent upward in planes parallel to the faces of 



Figure 6. 



