690 ATMOSPHERIC REFRACTION AT LOW TEMPERATURES. 



and Lieut. Foster, and the result in the last column of the 

 table is deduced from the mean of both. The distance of the 

 muzzle of the gun from the place of observation, as measured tri- 

 gonometrically by Lieut. Foster, was 12,892 • 82 feet, and by Capt. 

 Parry (by a different series of triangles). 12,892-96. The mean 

 distance employed in the calculation is 12,892' 89 feet. The bear- 

 ing of the gun was S. 71° 48' E. The observations appear to 

 indicate a decided decrease of velocity, with an increased density 

 of the atmosphere, the rate of travelling decreasing from 1,098 feet 

 per second, at a pressure of 30' 118 in., and temperature +33 '5°, 

 to 1,014 feet per second, at a pressure of 30-398 in., and tem- 

 perature — 38*5°, all other circumstances being alike. The last 

 experiment in the table shows a still greater velocity at a high 

 atmospheric temperature, which, however, might have been 

 influenced by a stronger breeze blowing from the direction of the 

 gun at that time. 



Date 

 . 1824, 



p 



1 



Wind. 



Weather. 



d 



Interval in Seconds 



betwen Flash and 



Report. 





Direc- 

 tion. 



Force. 



ia^ 





P. 



F. 



Mean. 



III 

















s. 



s. 



s. 





Nov. 24 - 



29-841 



-7° 



E.S.E. 



Light 



Overcast - 



5 



12-3525 



12-430 



12-3912 



1040-4^ 



Dec. 9 



22-561 



-9 



N.N.E. 



Squally 



Very clear 



6 



12-331 



12-5266 



12-4288 



1037-34 



Jan. 10, 1825 



30-268 



-37 



E.S.E. 



Light 



Clear 



4 



12-5889 



12-4700 



12-5290 



1029-04 



Feb. 7 



29-647 



-24-5 



N.E. 



Light 



Very clear 



6 



12-639 



12-6167 



12-6278 



1020-99 



Feb. 17 - 



29-598-18 

 29-735-37-5 



Calm. 



Overcast - 



6 

 6 



12-372 

 12 8167 



12-440 

 12-7067 



12-406 

 12-7617 



1039-25 



Feb. 21 - 



Calm. 



Overcast - 



1010-28 



March 2 - 



March 22 - 

 June 3 



30-398 

 30-258 

 30-118 



-38-5 

 -21-5 

 + 33-5 



E. 

 W. 

 E. 



Light 



Light 



Light 

 Strong 



and 

 squally 



Little over- 

 cast. 



Very clear 

 and fine. 



Very clear 



6 

 6 

 6 



12-640 



12-40 



11-7333 



12-780 

 12-7167 

 11-744 



12-710 



12-5583 



11-7387 



1014-39 

 1026-64 

 1098-32 



June 4 



30-102 



+35 



S.E.-5 



V Clear - 



6 



11-5889 



11-4733 



11-5311 



1118-10 



13. Determination of the Velocity of Sound at Low Tem- 

 peratures. (Second German Expedition.) 



Observations were made at a point of Walross Island and at 

 the cairn containing the records of the Expedition at Sabine 

 Island, the distance being 2091-21 metres. 



One observer was stationed at each point with a gun and a 

 chronometer, and each observer noted the instant at which the 

 gun was fired, and the time at which the sound was heard. 



