38 



gold leaf and elder pith, furnished with con- 

 ductors four feet long, to collect, according to 

 the method prescribed by Mr. Volta, the elec- 

 tricity of the atmosphere, by means of an ig- 

 nited substance which yields smoke ; 

 A cyanometer by Paul. To give me the means 

 of comparing with some certainty the blue 

 colour of the sky, as it is seen on the summit 

 of the Alps and the Cordilleras, Mr. Pictet 

 had this cyanometer coloured conformably to 

 the division of that which Mr. de Saussure 

 made use of at the top of Mount Blanc, and 

 during his memorable abode at the Col du 

 Geant ; 



An eudiometer of Fontana, for nitrous gas ; with- 

 out strictly knowing how many parts of this 

 gas are necessary to saturate a portion of oxy- 

 gen, we may still precisely determine the quan- 

 tity of atmospheric azote, and consequently 

 the purity of the air, by employing, beside the 

 nitrous gas, the oxygenated muriated acid, or 

 a solution of sulphat of iron. Volta's eudio- 

 meter, though the most exact of any, is em- 

 barrassing for travellers, who traverse damp 

 countries, on account of the small electric dis- 

 charge, which the inflammation of oxygen and 

 hydrogen gasses requires. The most portable 

 eudiometrical apparatus, the most speedy and 

 most eligible in every respect, is that pub- 



