146 MEASUREMENT OF AN ARC ON THE 



Experiments for determining the expansion of the 

 old Chain. 



1802. 



Month. 



TIME. 



« 5 



c s 



O rise. 

 2P.M. 



rise. 



1 P.M. 

 O rise. 



2 P.M. 

 O rise. 

 2 P.M. 

 O rise. 



83,5 

 110,3 



85,2 

 110 



80,2 

 108,1 



83,3 

 111,3 



80 



REMARKS, 



Cloudy wea- 

 ther and 

 high 



winds du- 

 ring the 

 whole of 

 these 

 experi- 

 ments. 



It appears from these results, that the expan- 

 sion due to ] <* of the thermometer is less than what 

 has been allowed by experiments made in England^ 

 but this might arise from the thermometers, as they 

 were such as could be purchased in the shops, and 

 therefore most probably of the best kind. Great 

 care, however, was taken to watch the moment 

 when they stood the highest, and though they va- 

 ried from one another considerably at that time, 

 yet that variation was generally the same in equal 

 temperatures. 



The reductions from the hypothenuses to bring 

 them to the horizontal level, were made by num- 

 bering the feet from the old chain as they were 

 measured, viz. by calling 32 chains 3200 feet, 

 which would be 3200,115 feet by the new chain; 

 but this would produce no sensible error in the 

 versed sign of a very small angle, and on that ac- 

 count these decimals were not taken into the com- 



