NATURAL PHILOSOPHY. 141 



tion ; and it is manifest that the size of the particle must depend, 

 not only on the size of the vapor-polyhedron, but also on the re- 

 lation of the density of the vapor to that of its liquid. If the 

 vapor were li^ht, and the liquid heavy, other things being equal, 

 the cloud-particle would be smaller than if the vapor were heavy 

 and the liquid light. There would evidently be more shrinkage 

 in the one case than in the other; these considerations were found 

 valid throughout the experiment. The case of toluol may be 

 taken as representative of a great number of others. The specific 

 gravity of this liquid is 0.85, that of water being unity ; the 

 specific gravity of its vapor is 3.26, that of aqueous vapor being 

 0.6. Now, as the size of the cloud-particle is dh'ectly propor- 

 tional to the specific gravity of the vapor, and inversely propor- 

 tional to the specific gravity of the liquid, an easy calculation 

 proves that, assuming the size of the vapor pol5^hedra in both 

 cases to be the same, the size of the particle of toluol cloud must 

 be more than 6 times that of the particle of aqueous cloud. It 

 is probably impossible to test this question with numerical accu- 

 racy ; but the com^Darative coarseness of the toluol cloud is strik- 

 ingly manifest to the naked eye. The case is, as I have said, 

 representative. In fact, aqueous vapor is without a paiallel in 

 these particulars ; it is not only the lightest of all vapors, in the 

 common acceptation of that term, but the lightest of all gases 

 except hydrogen and ammonia. To this circumstance the soft 

 and tender beauty of the clouds of our atmosphere is mainly to 

 be ascribed. The sphericity of the cloud-particles may be imme- 

 diately inferred from their deportment under the luminous beams. 

 The light which they shed when spherical is continuous; but 

 clouds may also be precipitated in solid flakes ; and then the in- 

 cessant sparkling of the cloud shows that its particles are plates, 

 and not spheres. Some portions of the same cloud may be com- 

 posed of spherical particles, others of flakes, the difi'erence being 

 at once manifested through the calmness of the one portion of 

 the cloud, and the uneasiness of the other. The appearance of 

 such flakes reminded me of the plates of mica in the River Rhone 

 at its entrance into the Lake of Geneva, when shone upon by a 

 strong sun. — American Journal of Science and Arts, Sept., 1869. 



ZIRCONIA LIGHT. 



The news spread in England, through the medium of the scien- 

 tific newspapers, that a discovery had been made in France, which 

 would have the eft'ect of abolishing the lime light by substituting 

 zirconia for the lime cylinder. The advantages were stated to be 

 that zirconia is not eaten away by the oxyhj'drogen flame, and 

 that, when not in use, it does not absorb moisture and crumble to 

 pieces like lime ; also, that, in consequence of this stability, the 

 ordinary clock-work of oxyhydrogen lamps to turn the lime cylin- 

 der would be unnecessary with zirconia. It was further said, 

 that the zirconia gave more light than lime under the same oxy- 

 hydrogen flame. Considerable interest in the new invention was, 



