G. W. Hough on an Automatic printing Barometer. 55 
float into the mercury 0-010 of an inch; after which, the current 
was established, 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 disturb- 
ances, 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 appre- 
ciable amount, during a whole year or greater length of time. 
The following extracts from our record book will best illus- 
trate the stability of the mechanism. 
July The machine was “ blocked” for 6 hours. Durin 
this time, the barometer rose 0:070 of an inch. After the float 
assumed its position of equilibrium, the zero of the machine, by 
comparison with the standard, was found unchanged. 
_ July 20th. The float was screwed up and down 0:200 of an 
Inch, to see if there was any friction. After assuming its position 
of equilibrium, the zero was found unchanged. 
ug. 17th. Float taken out of the barometer tube to put in 
a heavier platinum wire. The zero was changed 0°005 of an 
inch; mostly due to the larger wire displacing a greater amount 
of mercury. , 
_ The daily comparison of the pion records, with the read- 
ings obtained from the standar 
the months of J une, July and August. 2 
The 1st column indicates the hours: 0 hours _ 
The next three columns exhibit the mean height at eac 
for the whole month. The 5th column is the mean for the thre 
months, These numbers are thousandths of inches; the integer 
Inches being 29. | oar 
Tn reducing these observations, 4 days in June were rejected 
because the records were incomplete. those days the ma- 
chine was disturbed to make some alteration, or failed to per- — 
noon. 
hour, 
