Royal Society. '^Hl 



readily fusible, and that in its reduction from the chloride of alu- 

 minum by means of potassium, it presents itself in the form of fused 

 globules, generally so small that their shape is not distinguishable 

 under the microscope, although occasionally they are met with 

 having a sensible diameter. He effects the reduction at once in a 

 clay crucible, the bottom of which he covers with pellets of pure 

 potassium, and places upon these the chloride of ammonium, covering 

 the whole with chloride of potassium in powder. The crucible being 

 then closed up, and heated in a coal fire, the reduction is instantly 

 effected. 



Fused aluminum has the colour and lustre of polished tin ; it con- 

 tinues perfectly white in the air; it is fully malleable, and the glo- 

 bules may be beaten out into the thinnest plates without cracking 

 at the edges. It is entirely unmagnetic. In other respects the 

 metal in this compact state has the properties which the author for- 

 merly ascribed to it. 



March 6. — " Essays on Hygrometry and Barometry." By Captain 

 Shortrede, F.R.A.S., First Assistant in the General Trigonometri- 

 cal Survey of India. Communicated by Lieut.-Col. W. H. Sykes, 

 F.R.S. 



This paper commences with an account of the various investiga- 

 tions of the author on subjects relating to the elasticity of aqueous 

 vapour at different temperatures and under different circumstances. 

 He first discusses the tables given by different experimentalists of 

 the force of vapour at various temperatures, and endeavours to de- 

 duce an analytical formula giving the nearest approximation to the 

 results recorded. He then proceeds to the consideration of what he 

 terms " the moist bulb problem," or the point of maximum depres- 

 sion attained by a thermometer with a moistened bulb exposed to 

 evaporation in air: he deduces formulae which he compares with the 

 results of actual observation, and points out the probable sources of 

 error in the cases in which he finds disagreements between them. 

 In the miscellaneous remarks which form the next section of the 

 paper, the author states his reasons for dissenting altogether from 

 the views taken by Dalton of the constitution of mixed gases, or of 

 mixtures of aqueous vapour with any of the gases, according to 

 which, each gaseous body is uniformly diffused throughout the 

 whole space, its particles repelling those of its own kind, but exert- 

 ing no pressure on the particles of any other kind. He considers 

 the fact that a given poi'tion of air has its volume expanded by the 

 addition of aqueous vapour, as being of itself a sufficient refutation 

 of that theory. The author then takes occasion to discuss the ques- 

 tion, whether aqueous vapour exists in the atmosphere in the state 

 of mechanical mixture or of chemical solution, and argues in favour 

 of the latter view of the subject. 



In the concluding section, the author enters at large into the in- 

 vestigation of the method of ascertaining heights by barometric ob- 

 servations, and gives various tables to be used for that purpose. 



Afiop^uiTu, No. 2. " On the Epipolic Dispersion of Light ; being 

 a Supplement to a paper entitled < On a case of Superficial Colour 



2 H2 



