Registering and Printing Barometer. 



17 



with the standard. The new apparatus can be treated 

 precisely in the same manner as a pendulum. The stand- 

 ard barometer may be allowed to remain in the same tem- 

 perature, while the new apparatus is subjected to a degree 

 of heat sufficient to get a variation of 50° Fahrenheit. 

 A comparison of the printed results with the standard will 

 indicate the exact compensation necessary for the whole 

 apparatus. After the compensating rods are applied, the 

 experiment can be repeated until the adjustment is per- 

 fect. 



Numerous experiments have been made to test the sta- 

 bility of the float and magnetic connections. It will hardly 

 be necessary to give the results in detail. In case there 

 was no friction of any kind, the float ought always to 

 assume the same position for the same height of the mer- 

 curial column. The following is the test we have applied. 

 The electrical contact being broken by the key I, fig. 3, 

 the screw S was turned so as to force the float into the mer- 

 cury 0.010 of an inch; after which, the current was estab- 

 lished, and the float was allowed to take up a position of 

 equilibrium. The same thing was repeated, by turning the 

 screw in the opposite direction and lifting up the float. From 

 many trials, it was found that there was rarely a difference 

 of 0.002 of an inch, and usually less than 0.001 of an inch, 

 from the original position. The same test was applied for 

 larger disturbances, viz. 0.020 or 0.030 inches, with nearly 

 similar results. This is not a fair test, however, since 

 these conditions are never realized in practice. From all 

 our experiments so far, we see no reason why the machine 

 should change its zero any appreciable amount, during a 

 whole year or greater length of time. 



[Trans. vJ] 3 



