82 Prof. A. Connell on a new Hygrometer 



is cemented at C into a little brass stopper fitted by grinding 

 into the neck of the little bottle so as to be air-tight. D is a 

 small exhausting syringe of brass, the cylinder of which is 5 

 inches long by about j^ths of an inch wide. To prevent the 

 heat produced by the friction attending the working of the piston 

 being communicated to the bottle, the terminal valve of the 

 syringe is inserted in a collar of ivory, NO. The aperture in the 

 portion of this ivory piece to which the valve is attached is at 

 least yyth of an incn in diameter, that of the remainder of it is 

 y'^ths of an inch. The syringe must effect its purpose of exhaust- 

 mg in as perfect a manner as an instrument of that size can 

 accomplish. FG is a clamp of brass capable of being attached 

 by the screw horizontally to a window-sill in the position which 

 it occupies in the figure, or vertically to a common table. The 

 syringe screws into this clamp at K by a projecting screw sol- 

 dered to the former, when the clamp is screwed to a window-sill, 

 as is the case when an observation is made at an open window ; 

 or this projecting screw is inserted at L when the clamp is fast- 

 ened to a table, as is done when the experiment is made in a 

 room. In both cases the syringe itself occupies a horizontal 

 position, and the little bottle and thermometer of course a ver- 

 tical one ; the projecting screw K should be so constructed as to 

 cause the syringe to inchne with the bottle a little downwards, 

 so that the tendency of any aether to pass from the bottle into 

 the syringe may be counteracted, and any trace of it which 

 should pass into or be condensed in the syringe shall run back 

 into the bottle. The two surfaces of the portions of the clamp 

 which grasp the fixture ought to be well roughened that their hold 

 may be secure. 



Let us suppose the instrument fixed at an open window on the 

 sill. We of course note the barometer and the temperature of 

 the external air at the time ; and it is convenient, if a wet-bulb 

 thermometer happens to be at the window, to observe the amount 

 of the cold of evaporation at the time, because it gives an idea 

 of the point near which the dew-point may be expected, although 

 of course such an observation is by no means essential. 



A half-ounce measure graduated into drachms is then filled 

 with good commercial sulphuric sether to the extent of three 

 drachms of the liquid. This is slowly and carefully poured by 

 a proper lip in the measure into the bottle, the other hand being 

 held so as to prevent any interference with this operation from 

 any draft or wind, and the thermometer is immediately inserted 

 in the bottle and the stopper properly fixed. The process of 

 exhaustion is then begun, at first slowly, by working the piston 

 by one of the fingers of the right hand, so as to produce a gra- 

 dual cooling agency and equable distribution of the effect, and 



