Notes on Barometer Construction. 35 



Art. VIII. — Notes on Barometer Construction. 

 By George Foord, F.C.S. 



[Read 12th July, 1877.] 



At the last ordinary meeting of the Society my name was 

 on the list for reading an account of a proposed new form 

 of barometer — a somewhat free translation of a paper 

 appearing in a recent number of Poggendorff's Annalen — 

 it being understood that papers possessing this degree of 

 originality may from time to time be brought upon their 

 own merits under the notice of the Society. For want of 

 time the reading was postponed, since which postponement 

 it has occurred to me that there were other proposed forms 

 of barometer which it might be also interesting to consider ; 

 moreover, that a few hints concerning barometer tubes, and 

 the precautions to be observed in selecting, preparing, and 

 filling them — points which have fallen within the range of 

 my own personal experience — might prove useful. Most of 

 those who follow physical inquiries in the colony find the 

 necessity of at times helping themselves, often to the extent 

 of repairing, and occasionally of constructing, the instruments 

 upon which their work depends ; and therefore it is believed 

 that an interchange of views and experience concerning 

 minor details of construction — such as those now offered — 

 may not be wholly devoid of interest, 



I will then, with your concurrence, proceed in the first 

 place to give a few hints calculated to assist those who may 

 choose for the first time to try their skill in barometer 

 building ; and I will afterwards make reference to the forms 

 of barometer proposed respectively by C. Bohn, by Guthrie, 

 and an old proposition of Descartes incidentally mentioned 

 in Mr. Guthrie's paper, and which is not dissimilar in prin- 

 ciple to a form brought under the notice of our Society last 

 session, and which originated with Mr. Venables. 



First, then, as to the glass tube to be used. Its selection is 

 a matter of primary importance. Callipers or gauges will 

 enable us to ascertain how far the bore of a glass tube^ other- 

 wise applicable to our purpose, is of the same diameter at the 

 two ends ; for such gauges we may use very taper cones of 

 copper or brass_, or acute-angled plates of copper, brass, oi' 



