72 



BULLETIN OF THE UNIVERSITY OF WISCONSIN 



DETERMINATION OF Y. 



Instrument. Circle R. Circle L. 



Levelled ........ 180 26' 49" 358 4' 13* 



Deflected ....... 179 27 3 359 3 48 



= 59' 40.5* 



z. 



91 11' 18" 

 90 11 37.5 



After the level readings which follow were completed, 

 these circle readings were repeated with the instrument 

 deflected and subsequently leveled, giving a second deter- 

 mination of y = 59' 42". I adopt : 



y = 59' 41' 



The following are the bubble observations in the de- 

 flected position of the instrument: 



The observations began with the level bubble at one end 

 of its scale, circle reading 111 34', and the instrument 

 was turned through successive intervals of 10' until the 

 bubble reached the opposite end, when the settings were 

 repeated in the inverse order to eliminate the effect of any 

 slight change in the instrument or level. The instrument 

 was then turned into the position corresponding to the 

 second set of circle readings which were taken with the 

 bubble running from one end of the tube to the other, 

 in both directions. 



The mean of the four readings of the ends of the bubble 

 corresponding to any circle reading may be adopted as the 



