BY HEAT OF METALS AND ALLOTS. 881 



expansion of air given 0-003665 for each degree of the mercury-thermometer, which is 

 not correct; for as air expands regularly between 0° and 100° according to the air-ther- 

 mometer, a unit of volume of air measured at 0° will not occupy a volume at 20-14 mer- 

 cury-thermometer equal to 



l-f0-003665x20-14=l-07380, 

 but 



1+0-003665 X 20=1-07330, 



showing a difference of 0*05 per cent. 



Miller, in his paper already mentioned, p. 714, says, " Reqnault found the expansion 

 of air from 0° to 100'' under constant pressure equal to 0-36706 of its volume at 0°.. . .The 

 difference between the mercurial and air-thermometers amounts to about 0-2. Hence 

 the expansion of air between 0° and 50°-2 is 0-18353 of its volume at 0°; or between 0° 

 and 50° the ratio of the density of air at 0° to its density at ^ is 1 +0-003656 X i" 



In the present state of science it seems quite wrong that such a want of accordance 

 should exist in our normal instruments, considering that otherwise the errors that exist 

 between the instruments do not amount to 0°-l when properly made. I have had several 

 normal thermometers made for my experiments by Messrs. Negeetti and Zambra, and 

 in every case, when compared with my Kew Standai-d, the agreement between them 

 has been almost perfect. 



It would be decidedly a step in the right direction if in future the fact that mercury 

 does not expand regularly between 0° and 100° were taken into account in the con- 

 struction of all normal thermometers; and if some comparisons between the Kew 

 Standard and the air-thermometer were made, then the readings of thermometers which 

 have been compared with the Kew Standard might be easily corrected. 



Jolly *, in his research into the expansion of water, corrected his thermometers by 

 comparing them with an air-thermometer ; unfortunately, however, he does not give a 

 table containing these comparisons ; so that his results are obviously not comparable with 

 those obtained with the mercury-thermometer, and therefore at present I am unable to 

 compare his results with those obtained on the same subject by myself. In conclusion, 

 my thanks are due to Dr. M. Behrend for carrying out the determinations for the 

 Series 1, 2, 13, 20, 21, 24 to 27 and 34, to Mr. Bassett, who aided me in carrying out 

 the others, and to Mr. R. P. Wright for having undertaken the greater part of the com- 

 putations. 



* Berichte der K. b. Akad. der Wissench. ivl MiincheD, 1864, p. 141. 



