20 



Dr. A. M. Mayer on an Acoustic Pyrometer. 



number arrived at by Magnus and Kegnault for the expansion of 

 air under a constant pressure; and this is one of the most re- 

 liable constants we have in physics. Hence the accuracy of our 

 measures to 10° C. will be equal to those of the air-thermometer, 

 whose indications at present are necessarily received as our 

 standards of thermometric determinations. 



We will now examine the relation existing between tempera- 

 tures and wave-lengths. I here give two Tables : the first con- 

 tains the velocities of sound and the wave-lengths of the note 

 ut 4 corresponding to temperatures between 0° C. and 2000° C. ; 

 the second, those corresponding to temperatures between 0° C. 

 and -272°-48 C. 



Temperatures. 



Velocities. 



Wave-lengths. 







metres. 



metre. 



DC. 



333 



0-650 



100 



389-34 



0-760 



200 



438-53 



0-856 



300 



482-72 



0-942 



400 



52314 



1021 



500 



560-74 



1-095 



600 



596-03 



1-164 



700 



62904 



1-228 



800 



66067 



1-290 



900 



690-77 



1-349 



1000 



719-64 



1-405 



1100 



747-38 



1-458 



1200 



77419 



1-512 



1300 



799-96 



1-562 



1400 



82494 



1-611 



1500 



849-35 



1-658 



1600 



872-96 



1-705 



1700 



895-97 



1-748 



1800 



918-41 



1-793 



1900 



940-26 



1-836 



2000 



961-70 



1-878 









333 



0650 



- 50 



300-86 



0-587 



-100 



265-00 



517 



-150 



22314 



0-435 



-200 



171-79 



0-335 



-250 



95-60 



0-186 



-272-48 



00-00 



0-000 



These related numbers I have projected into the accompanying 

 curve (PL III. fig. 8), whose abscissae are the temperatures, and 

 whose ordinates are the wave-lengths. This curve, which is the 



.. i c 333 VT+ '00367 x 

 graphical expression of y- — — } 1S evidently a 



512 



