We are indebted to Mr. Max Kuner, nautical opticia 94 Columbia street, Colman building, Seattle, for t following interesting description of the standardizing the Aneroid barometer as daily practised by him:
"The apparatus used by us consists of two mercurial column barometers, and an air pump with mercu column attached. The two mercury barometers we first standardized in this manner:-They were car fully corrected for capillary attraction by moving t scale to the proper point. Then as a constant err there was an error for height above sea level to subtracted. An error for local gravity to be adde These are constant error. There remains the temper ture error; this is a variable one. (All barometers the U. S. are reduced, for purposes of comparison, 32 degrees Fahrenheit, sea level, local gravity, as Washington, D. C). Our two barometers are compar each day at 5 p.m., and after subtracting the algebra: sum of the errors are compared with the Weather B reau. reading, thus preventing all chance of error. (V have never got a variation, both barometers readi alike in every case).
"The method of testing is as follows: the corre height of the mercury column is read off both baron ters, and the correction for temperature subtracted. the aneroid is compensated it corrects for temperatu and so reads different from our standard. The m< cury column on the machine is set to read this heig by shifting the scale. The aneroid to be tested is s to the same reading and placed under the bell glass the air exhausted. Every half-inch the column and the aneroid are compared and the aneroid's error, if an noted. When the limit of the aneroid's scale is reach the air is allowed to enter slowly and the reading and error noted going up the scale. The aneroid then go out with our written certificate and its character an faults are known to the user, thus making it a depend-able instrument. Without this precaution the aneroid is a mere guessing machine, but when properly cc reeted is an instrument of the utmost delicacy and accuracy, ranking above the sympiesometer and the mercury column. This is especially true of the mode holosteric compensated aneroid (Holosteric means flat spring, and is used in contradistinction to the old spiral spring aneroid). If there are errors of adjus-ment, we carefully correct these, in order that naviga-tors may have a dependable instrument. This method of standardizing is identical with that practised in the observatory of the National Physical Laboratory. Kew observatory, England."