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XXXIX. 



ON A MEKCUEY-GLYCEEINE BAKOMETER. 

 By J. JOLY, M.A., D.Sc, F.R.S. 



[Eead April 20, 1892.] 



A COLUMN of mercury may be suspended unbroken in a wide 

 tube — it appears immaterial how wide — by a device which, occurred 

 to me some seven or eight years ago, and which was then brought 

 by me before the Dublin University Experimental Science Associ- 

 ation. I have heard lately that the arrangement is not new, but 

 when or by whom else invented seems unknown. The arrange- 

 ment is as follows: — A cylinder of ivory or ebonite, having a 

 diameter a little less than that of the tube, has a projecting 

 "float" extending from its centre at one side (see fig. A). The 



shank of the float may be a steel pin, and the float a sphere or 

 cylinder of wood or ivory. Now, if the float enter the bottom of 

 a column of mercury, contained in a wide tube, it will tend to rise 

 through the mercury and will pull the cylinder up against the 

 base of the column with a force equal to the difference in weight 

 of the float and the mercury displaced by it. But if the float has 



SCIEN. PROC. K.D.S. — VOL. VII., PART V. 



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