1880.] On the Constimction of a Glycerine Barometer. 107 



and on their recommendation a grant of £30 was made by the Trea- 

 sury for the purpose. This sum has been expended in the construc- 

 tion of an experimental barometer of this nature, which has been 

 erected at Kew Observatory by the permission of the Kew Committee, 

 who have also sanctioned the taking of a series of observations to 

 extend over a period of twelve months. 



The tube forming the body of the instrument is an ordinary com- 

 position metal gas-pipe, f-ths of an inch internal diameter, and furnished 

 at the top with a gun-metal socket, into which is cemented a glass 

 tube, 4 feet long, and having an inside diameter of one inch ; the upper 

 end is formed in the shape of an open cup and fitted at its neck with 

 an india-rubber stopper. In this tube the fluctuations of the posi- 

 tion of the top of the column are observed, and the height read of£ 

 on brass scales placed on either side of the tube and fitted with 

 indices and verniers, which are moved by means of milled heads 

 placed at the bottom of the scales as shown in the drawing at AA. The 

 scale on the right hand side is divided into inches and tenths of 

 absolute measure, numbering from the level of the liquid in the 

 cistern, while that on the left shows equivalent values reduced to a 

 column of mercury and divided into tenths and hundredths, each 

 hundredth being equal to about one- tenth of an actual inch. The 

 whole of the top fittings, or observing portion of the barometer, is 

 attached to a conveniently constructed back, made of oak and fixed 

 to the wall of an upper room in the observatory building, the main 

 tube being carried down in a direct line through the entrance hall 

 into the barograph room, a distance of 27 feet. This distance was 

 accurately determined by means of a tape measure, the error of which 

 was found by close comparisons with the standard yard preserved at 

 the Observatory. A suitable bracket is here fixed, on the north wall r 

 on which is placed the barometer cistern. 



The cistern is a cylindrical vessel of copper tinned inside, 5 inches 

 deep and 10 inches diameter ; it is fitted with a screwed cover, as 

 shown at B in the drawing, the air having access only through a 

 small hole in the cap C attached to the cover, which has a recess 

 in it to hold cotton wool for filtering out dust. The main tube is 

 connected with the cistern by attachment (with a soldered joint) to 

 a projecting piece of tube D, which enters the cistern through the 

 bottom and is fitted at its opening with a screwed plug E. 



The operation of filling the barometer was performed in the follow- 

 ing way : — The quantity of glycerine (coloured red by aniline) having 

 been previously determined, it was heated to a temperature of 100° F. y 

 to render it more limpid, thereby enabling the contained air to dis- 

 engage itself more freely ; the whole quantity, about three-fourths of a 

 gallon, was then transferred to the cistern, the plug B removed, and 

 by means of an air-pump connected with the top of the glass tube, the 



