Mr. T. Tate on a new Self-registering Mercury Barometer, 263 



medium which produces the irrationality, more correctly than 

 do the extrusions arising when only seven lines are taken into 

 the account. But this point cannot be satisfactorily ascertained 

 until recourse be had to such a method of experiment as shall 

 exhibit the irrationality apart from the dispersion. 



Indeed it is manifest that, for the further elucidation of the 

 laws of refraction and dispersion, it is needful to resort to a 

 totally different method of experiment from what has been 

 hitherto pursued, and to adopt such arrangements as shall pre- 

 sent the effects of the refractive, the dispersive, and the extrusive 

 powers of the medium, each separately and distinctly. The 

 variations of each power, produced by change of temperature, 

 may then be studied with some reasonable prospect of arriving 

 at precise and satisfactory results. 



XXXII. On a new Self-registering Mercury Barometefi\ 

 By Thomas Tate, Esq.* 



[With a Plate.] 



THE advantage of this instrument consists in the extent of 

 its range as compared with that of the common barometer, 

 and in its adaptation for the purpose of self-registration. It 

 differs from the common barometer in having a floating cup, 

 which rises or falls according as the column of mercury, balan- 

 cing the pressure of the atmosphere, falls or rises, thereby pro- 

 ducing an increased variation in the level of the mercury in the 

 tube for any given change in the atmospheric column. The 

 construction of the instrument is shown in Plate III. fig. 3, 

 L K D is the barometer-tube fixed to the frame A B, having its 

 lower or open extremity, D, inserted in the mercury, I F, con- 

 tained in the glass float EGF; Q N a glass jar containing water 

 slightly acidulated with sulphuric acid to arrest the evaporation 

 from its surface. The glass float consists of two tubular por- 

 tions, E M, open at the top, and I F closed at the bottom, and a 

 globe G to give a force of floatation sufficient to balance the gra- 

 vity of the mercury contained in the tubular portion I F ; a light 

 cap, with projecting arms a and b, is attached to the top of the 

 tubular portion M E, to keep the float in position and to give 

 motion to the indices of registration ; b is a small weight touch- 

 ing the upper face of one of the projecting arms, and balancing 

 the index weight d by means of a fine thread or hair passing 

 over a wheel e ; in like manner a is a small weight whose upper 

 surface touches the under face of the other projecting arm ; the 

 index d registers the maximum pressure of the atmosphere, and c 



* Communicated by the Author. 



