1880.] On the Construction of a Glycerine Barometer. 105 



III. " On the Construction of a Glycerine Barometer." By 

 James B. Jordan. Communicated by Professor Stokes. 

 Sec. R.S. Received January 8, 1880. 



Various attempts have been made from time to time to construct 

 barometers with fluids of lower density than mercury, with the view 

 of increasing the range of movement of the column by the direct 

 action of the atmosphere, thereby rendering the variations of pressure 

 more easily visible, without the intervention of mechanical appliances. 

 I have been induced to give the subject attention in the belief that if 

 precise instruments of this class could be made they would prove of 

 scientific value in showing the character of the more minute vibrations 

 of atmospheric pressure, and of practical use at storm stations, 

 collieries, and other situations where it is of importance for the un- 

 practised eye to notice frequently the movements of the column with- 

 out the careful observation necessary in the reading of an ordinary 

 mercurial barometer. 



Water is apparently the most convenient liquid for a long range 

 barometric column, and many water barometers have been constructed, 

 notably that made for the Royal Society in 1830, by Professor Daniell. 

 A water column is, however, of little use for indicating variations of 

 pressure, owing to the effect of changes of temperature on the water 

 vapour existing in the Torricellian vacuum, which often masks the 

 effects which would otherwise be produced by changes of pressure. 

 Having successfully constructed several water barometers, and finding 

 this conflicting action caused by variations of temperature so detri- 

 mental to their value, I was induced to experiment with other liquids, 

 and among those tried pure glycerine appeared to me to answer the 

 purpose best. Glycerine from its high boiling point has a very low 

 tension of vapour at the ordinary temperatures of the atmosphere; 

 the length of the column is therefore only altered from changes of 

 temperature by expansion and contraction of the liquid itself, and 

 that in a very small degree, the mean coefficient of absolute expansion 

 between 0° and 100° C. being -0005455. The specific gravity of the 

 purest glycerine as manufactured by Messrs. Price and Co. is 1*26, or 

 less than one-tenth that of mercury ; the mean height of the column 

 is 27 feet at sea level, and a variation of a tenth of an inch in the 

 height of the mercurial column is shown by a change of more than 

 an inch in the glycerine ; the boiling point is 440° and a very low 

 temperature is required to solidify it. As glycerine absorbs moisture 

 freely if exposed to the atmosphere, the action is prevented by 

 covering the surface of the liquid in the cistern with a shallow layer 

 of heavy petroleum oil, prepared especially for the purpose. 



In order to give the method a fair trial, application was made to 

 the Committee of the Government Fund for aiding scientific research, 



