SCIENTIFIC SUMMARY. 
185 
subjected 83 substances, of which 8 were metals, 6 metalloids, 10 oxydes 
and sulphides, 32 salts, and 19 carbonaceous bodies, with 8 mechanical 
mixtures, to compression, either under ordinary or elevated temperatures, 
with the following among other results. Lead in a vacuum, under pressure 
equal to that of 2000 atmospheres, becomes as solid as when melted ; under 
5000 it flows like a liquid. Bismuth welds easily under a pressure of 6000 
atmospheres, breaking afterwards with a crystalline fracture. Pewter 
behaves like lead. Zinc requires 5000 atm. Aluminium and copper unite 
at 6000 atm. Antimony in grey powder recovers solidity and metallic 
lustre at 5000. Platina welds imperfectly with pressure alone. Of the 
three allotropic forms of sulphur, the transparent prismatic form at 
5000 atm. became harder than that obtained by fusion, and probably 
octahedral, a form which the plastic variety also took at 6000 atm. 
The octahedral form itself welds easily at 3000 atm. Amorphous carbon 
refuses to solidify under any pressure whatever, and exhibits the most 
perfect elasticity. Graphite, on the contrary, as is well known, agglome- 
rates to a solidity equal to the native material. Peroxyde of manganese 
took the exact appearance of crystalline pyrolusite. Alumina became 
translucent, like the mineral known as Halloysite, flowing like a liquid, but 
showing no tendency to assume the form of corundum. Sulphide of lead 
became galena. Many chlorides, bromides, and iodides welded and became 
transparent. Mercuric iodide took a violet colour. Nitrate of potash 
became plastic like wax at 3000 atm., as did hyposulphite of sodium. 
Glass resisted at every pressure. Turf became practically coal, losing all 
trace of organic structure, and coking in a close vessel just like coal, a 
result of some geological importance. 
Pressure was also found to influence chemical combination. For 
instance, under a pressure of 5000 atms. sulphur and metallic copper com- 
bine perfectly. Mercuric chloride and the same metal change places, 
metallic mercury and cuprous chloride, free from cupric chloride, being left. 
M. Spring points out (1) that under compression, the attraction of 
particles follows the direction of the crystalline axes ; (2) that crystalloids 
coalesce better than amorphous bodies ; (3) that after welding, many bodies 
reputed solid flow like liquids. The compressing apparatus is described as 
consisting either of screws or powerful levers weighted at their end. 
Hydraulic compression is not alluded to. 
Musical pitch and its determination formed the subject of a recent 
lecture at the Royal Institution by Dr. W. H. Stone. He pointed out that 
absolute pitch does not exist in nature, the exceptional power of recog- 
nizing a note, or hearing it, being really an acquirement connected with the 
‘ muscular sense’ in singers, and musical memory highly developed in 
organists and instrumentalists generally. After defining pitch as rapidity of 
vibration, he considered (1) the causes and amount of variation in different 
sound-producers ; (2) scientific methods of measuring pitch ; (3) the musical 
application of such methods. 
1. Heat variations were illustrated by metallic strings, organ-pipes, har- 
monium-reeds, and tuning-forks. 
2. The mechanical, optical, photographic, electrical, and computative 
methods of determining pitch, were exhibited and explained. These included 
