1892.] on Metals at High Temperatures, 503 



A great step in advance was made in 1701 by Sir Isaac Newton,* 

 who applied the law of cooling to the measurement of temperatures 

 beyond the range of the mercurial thermometer, and in the notes 

 which accompany his " Scala graduum caloris " he showed that he 

 knew that the freezing-point of lead differs slightly from its melting- 

 point. 



Eighty years later, Josiah Wedgwood (1782), f aided by one of 

 my predecessors, Mr. Alchorne, Assay Master of the Mint, deter- 

 mined a few melting-points of metals, and, in communicating a 

 description of his " thermometer for measuring the higher degrees of 

 heat" to the Eoyal Society, we find him, one thousand years after 

 Geber had said that " fire cannot be measured," still lamenting the 

 want of suitable instruments, saying : " How much it is to be wished 

 that the authors (to whom he refers) had been able to convey to us a 

 measure of the heat made use of in their valuable processes ; . . . 

 a red heat, a bright red, and a white heat are," Wedgwood adds, 

 *' indeterminate expressions, and even though the three stages are 

 sufficiently distinct from each other, they are of too great latitude, 

 and pass into each other by numerous gradations which can neither 

 be expressed in words nor discriminated by the eye." Another 

 ninety years brings us to the last time that the measurements of high 

 temperatures formed the subject of a Friday evening discourse in 

 this Institution. On March 1st, 1872, the late Sir William Siemens 

 addressed you on the measurement of " heat by electricity " ; ^ and, 

 speaking of the mercurial thermometer, said : " When we ascend the 

 scale of intensity we soon approach a point at which mercury boils, 

 and from that point upwards we are left without a reliable guide, and 

 the result is that we find, in scientific books on chemical processes, 

 statements to the effect that such and such a reaction takes place at a 



* dull red,' such another at a ' bright red,' or a ' cherry red,' or a 



* white heat,' — expressions which remind one," he adds, "of the 

 days of alchemy rather than of chemical science at the present day." 



It is not a little singular that the same lament should have been 

 uttered, with so long an interval between, by two prominent technical 

 men, and it suggests that but little experimental work had been done 

 in the meantime with a view to the measurement of high temperatures. 

 This is, however, far from being the case. A vast amount of work 

 was done by physicists and metallurgists whose chief masters were 

 " indefatigable labour, the closest inspection, and hands that were 

 not afraid of the blackness of charcoal " ; and their more noteworthy 

 efforts were based on the employment of the air thermometer, in 

 which the expansion of air replaces the expansion of the mercury in 

 the ordinary thermometer, the bulb being of some fire-resisting 

 material.§ For this purpose, Princep (1827) used a bulb of gold, 



» 'Phil. Trans. Eoy. Soc' vol. xxii. p. 824. f Ibid. vol. Lsxii. p. 305. 



t ' Eoy. Inst. Proc' vol. vi. p. 438, 1872. 



§ See the excellent bibliography given by C. Barus, ' Bull. Geological Survey, 

 U.S.A.' No. 54, 1889. 



