48  SsLIDING-SCALE FOR CORRECTING BAROMETER READINGS. 
barometer or the nearest reading to it was found ; opposite thisa 
mark was made on the scale and “ Bathurst” written on it. Now, 
whenever the same reading is received, the scale being placed as 
before, the marks opposite Bathurst would show the corrected 
reading ; and since the readings in the columns increase at the 
rate of 0-01, any other reading being given with the same tempera 
ture, the same scale would serve to point out the corrected reading 
required. 
The table thus prepared was placed upon a cylinder, so that any 
part of it could be immediately brought up for inspection, and the — 
scales (some forty-six—one for each degree of temperature) were pre 
and promised a very great saving of time; but in 
variation in the atmospheric pressure. The result is the com 
venient sliding-scale represented in the annexed photo-lithograph. 
. 
to begin at 28 inches, in order to reach the high stations. A 
taken, and corrected for index error for the temperature of en ; 
and for altitude; the barometer scale on a strip of pape @ 
“corrected” reading as by computation was found, and 
| made. Exactl 
upon it the corrected readings of the barometer for any ' 
‘ any troublesome extent. The use of this scale 
