io8 



NATURE 



[yime 6, 1872 



ture of 65° and 3,000°. Let us be careful not to confound this 

 increase of emissive power with the increase of radiant energy 

 resulting from nitre augmentation of temperature. It is, no 

 doubt, owing to the change of the molecular constitution of the 

 body during healing that the dynamic energy developed at a 

 differential temicrature of 3,000° is 421 times greater than it 

 should be in accordance with the Newtonian law — a trifling in- 

 crease, howevei, compared with that resulting from adopting 

 the tompulatio:is of Dulong and Petit, whose formula shows that 

 for the stated range of temperature the ratio of radiant energy 

 will be increased more than 4,000 times. It would be premature 

 to attempt to explain the cause of the cliange of the radiant 

 properties of netals at different temperatures disclosed by our 

 experiments, until further investigations shall have established the 

 exact relation between the .actual and theoretical energy de- 

 veloped. Considering the difference of molecular motion within 

 metallic bodies at white heat in a state of fusion, and at the 

 freezing point of water, we need not be surprised at the variation 

 of emissive power observed during our experimental investiga- 

 tion. Nor are we justified, in view of this variation of emissive 

 power, in questioning the correctness of Sir Isaac Newton's 

 assumption that heated bodies of definite radiant properties de- 

 velop mechanical energies proportional to their excess of tem- 

 perature over the surrounding media. 



89 



88 

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85 

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71 

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69 

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67 

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65 

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45 

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 43 



Seconds. 



1157-71 

 1193-16 

 1229-27 

 1266-06 

 1303-56 

 1341-79 

 1380-79 

 1420-59 

 1461-22 

 1502-71 

 1545-10 

 1588-43 

 1632-75 

 1678-10 

 1724-53 

 1 772 09 

 1820-84 

 187084 

 1922-16 

 1974-86 

 2029 02 

 2084-73 

 2142-08 

 2201 17 

 2262-11 

 2325-01 

 2390-01 

 2457-25 

 2526-89 

 2599-11 

 2674-11 

 2752-11 

 2833-36 

 291814 

 3006-78 

 3099-64 



3197-14 

 3299 77 

 3408-10 

 3522-80 

 3644-67 

 3774-67 

 3913-95 

 4063-95 

 4226-45 

 4398-73 

 4593-73 



Seconds. 



34-82 



35 '45 

 36-n 



36-79 

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39-00 

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 4063 

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43-33 



44-32 

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50-00 



51-32 

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60-94 

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67-24 



69-64 

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75-00 



78-00 

 Si -25 

 84-78 

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97-50 

 1 02 -63 

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 1 50 00 

 162-50 

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 195-00 



J. Ericsson 



[^^'E have received a communication by cable from the author, 

 to the effect that theengraver has indicated, in Fig. 2, a continuous 

 space between the curves a l> and n c, whereas the space should 

 cease at one portion, the curves intersecting each other between 

 the ordinates 25 and 30. The mistake is so trifling that it can 

 scarcely be observed with the naked eye, yet it will no doubt be 

 detected by such men as Stewart, Maxwell, and Everett. It is to 

 be found, on looking at the table, that the observed times are 

 shorter than the calculated times at the high temperatures, while 

 the observed times are longer th.an the calculated times at low 

 temperatures; hence ihecurves must intersect each other. — Ed.] 



NOTES 



The Pal! Mall Gazette states that the Earl of Portsmouth, 

 who is the collateral representative of Sir Isaac Newton, has 

 offered to the University of Cambridge, through the Duke of 

 Devonshire (Chancellor of the University), all the papers of Sir 



