Art. IX. — Observations zvitJi Aticroid and Mercnrial 

 Barometers and Boiling Point Thermometers. 



By Thomas Walker Fowler, M.C.E., F.R.G.S. 



[Eead 10th October, 1895.] 



In connection witli engineering and general survey work, as 

 well as in geographical investigations, it is frequently conveni- 

 ent to determine, approximately, the attitudes of different points 

 from observations of barometric pressure at such points. Various 

 instruments are used for this purpose, the most convenient and 

 portable being, undoubtedly, the aneroid barometer, and the 

 most trustworthy, the mercurial barometer of either the Fortin, 

 or syphon type provided that the tube be of large bore. The 

 latter requirement causes the instrument to be veiy heavy and 

 neither portable nor convenient. Boiling-point thermometers 

 form a third-class of instruments much less convenient than 

 aneroid barometers, but decidedly more portable than mercurial 

 ones even of small bore, as all mercurial l^arometers are very 

 liable to damage from destruction of the vacuum through careless 

 handling as well as from fracture of the tube. Delicate and 

 fragile thermometers, undoubtedly, require careful handling, but 

 much less so than mercurial barometers. 



From 20th August last up to the present time, the writer made 

 a series of obsei-vations for the purpose of determining the 

 relative accuracy of instruments of the classes mentioned. They 

 were made at his residence in Upper Hawthorn, Melbourne, the 

 approximate altitude above sea level being 200 feet, and during 

 the observations the atmospheric pressure varied considerably, 

 the maximum recorded being 30"04S inches, and the minimum 

 29-020 inches. 



For use as a Standard the Acting Government Astronomer 

 (Mr. Baracchi), kindly placed at the writer's disposal a pedestal 

 mercurial barometer of the Fortin type, made by Newman k, Son, 

 and numbered 122. The diameter of the tube is mai-ked 0'380 

 inch. The adjustment of the fiducial point is made by raising 



