78 



THE SAY IMC OBSERVATORY. 



It was therefore determined to examine thoroughly these levels at intervals of three 

 months. As no important changes were found, they afterward received less frequent 

 attention, but the process was always repeated at least twice each year. 



hi this investigation the ordinary level-trier was employed, consisting of a, horizontal 

 bar with a micrometer screw at one end. The proportions in the present case were such 

 that one division of the micrometer head corresponded loan angle of L" in the inclina- 

 tion of the bar. 



The level tubes were placed in position, carefully protected from disturbances of all 

 kinds and allowed to remain for an hour or two in order to allow the temperature of all 

 parts of the apparatus to come to a, condition of equilibrium. The bubble, was then brought 

 near one end of the tube and the scale reading noted. The screw was next moved for- 

 ward two divisions and the scale again read, and so on through something more than the 

 entire part of the scale actually used in observation. 



The screw is now moved backward and the reading of the scale noted at the same 

 screw readings as before. From one to two minutes are allowed for the; bubble to come to 

 rest after moving the screw. If too much time elapses there is danger that changes of 

 temperature or other disturbing causes may vitiate the result. 



The process is illustrated by the following record of the determination of the value of A : 









Bubble. 





Bubble. 







'.11, April 1, 

 111. ISO A.M. 





Uterometer, 





Mcctn. 







Mfd.n. 



riiiTinome 



1 



N. 



a. 



20. 1 



L4.95 



N. 



,S'. 



L4.45 



Ler, 56°,4. 





71. 



8.8 



3.4 



25.5 







2 



00 



4.8 



27 1 



15.95 



4.6 



20.7 



15.05 







3 



07 



<i.:s 



28.0 



17.45 



0.2 



28.3 



17.25 







4 



05 



8.8 



80.6 



L9.45 



7.8 



20.0 



18.85 





•6 



5 



68 



i).8 



82. 1 



20.05 



0.4 



31.5 



20.45 



>Tl 





(i 



Gl 



II.:? 



33.0 



22.45 



1 



33. 1 



22.00 







7 



69 



18.0 



86.8 



2-1. 1 5 



12.7 



84.9 



23.80 



r 





8 



57 



14.7 



87.0 



25.85 



1 1.2 



86.4 



25.3,0 







9 



55 



10,1 



S8.-6 



27.50 



15.9 



38.1 



27.00 







10 



r,:; 



18.2 



'10.5 



29.85 



17.7 



89.9 



28.80 







II 



51 



19.6 



41.8 



30.70 



10.2 



41.4 



30.30 







12 



4!) 



21.0 



415.2 



82.10 



20.5 



42.8 



31.05 







18 



47 



22.7 



45.0 



88.85 



22.3 



44.5 



33,1(1 







14" 



48 



24.6 



45. 8 



85.70 



2:'.. 8 



40.1 



34.05 











8—1 



10.00 







10.85 











!)— 2 



LI. 55 







11.35 











10—3 



1 1 .00 







11.55 











11—4 



11.25 







11.45 











12—5 



11.15 







11.20 











18—6 



1 1 .40 







11.40 











14—7 



11.55 







11.15 











14" 



11.886 







11.270 











One. divisi 



)n = 



s 1".229 







1".241 





The same values of the levels were not employed throughout the entire latitude series, 



