Description of the Moujil am Barometer, 40 



I cannot, therefore, but hope, by simplifying the baro- 

 meter, and thereby rendering the instrument much less ex- 

 pensive, and its u?e at the same time more easy, and show- 

 ing that very considerable accuracy n)ay be attained by a 

 single observer, this most useful branch of science may be 

 cultivated, to so great an extent, that, in the course of a 

 few years, we may have almost as perfect an idea of the re- 

 lative heights CrF the dilfercnt j)arts of IJngland, as we now 

 have of their horizontal di/tance. 



A barometer, nearly similar to that which I am now 

 about to describe, was constructed, several years since, by 

 Dr. Hugh Hamilton, and is by him dcseribed at large in 

 the fifth volume of the Transactions of the Irish Academy. 

 I saw the instrument, in his hands, nearly seventeen years 

 ago, and was much pleased with its performance. I do not 

 know, however, that any more were then made. I have 

 lately coustructcd the barometer, whose description I shall 

 now give, which is still more simple than Dr. Hamilton's, 

 and much cheaper, and which, in many trials I have made 

 of it, appears tO' unite solidity, lightness, and ease of ob- 

 servation, to as great a degree as can be wished. 



The barometer lube is about 33 j inches in length ; its 

 bore is a teaih of an inch in diameter, and its external di- 

 ameter is three-tenths of an ir.ch. This sized bore is fullv 

 suflicient to allow the free motion of the mercury*. Tlie 

 \Mstern is of box-wood, turned truly cylindrical, 'aiid is one 

 inch in its external diameter, and an inch in depth; a short 

 stem projects from its lop (the instrument being in a posi- 

 tion for making an observation), for the purpose of giving 

 a firmer hold to the tube : this stem is perforated \yiih a 

 hole sufficiently large to admit the tube, which is glued to 

 it in the usual mode. The ttibe projects into the cistern 

 i 



* Several barometers haveliecn lately constructed by Mr. Jones, with the 

 lower part of tlic tube only a iwe.itietfi of ;ui incti in bore, something on tlie 

 principle of the marine barometers. This alteration was made because ia 

 some few instances when very carelessly used, air had {^ot into the tube. In 

 the form now adopted, this defect seems compk-tely remedied, and the mo- 

 tion of the mercury, thonj^h full free enough for accuracy, »<> rendered so 

 equable, that observations in a carnage are much easier. 1 therefore, on the ■ 

 wliolc, prefer this construction. 



Vol. so; No. 117. Feb, 1608. D exactly 



