| Rapps | 1878 | 0 .65 |
| English Glass | 0 .15 | |
| Ver Deer | 0 .08 | |
| 16"' | 0 .05 | |
| 59"’ | 0 .02 |
ANALYSIS OF GLASSES.
| SiO2 | Na2O | CaO | Al2O3 | ZnO | B2O3 | |
| 16"’— | 67.5 | 14 | 7 | 2.5 | 7 | 2 |
| 59"’— | 72 | 11 | 5 | 12 |
Weber had found in 1883 that glasses which contain a mixture of soda and potash give a very large depression. He made in 1883 a glass free from soda with a depression of 0°.l. The work was then taken up by the Aichungs Commission, the Reichsanstalt, and the Jena factory. Weber's results were confirmed. An old thermometer of Humboldt's containing 0.86 per cent, of soda and 20 per cent, of potash had a depression of 0°.06, while a new instrument, in which the percentages were 12.7 per cent, and 10.6 per cent., respectively, had a depression of 0°.65. An English standard, With 1.5 per cent, of soda, 12.3 per cent, of potash, gave a depression of 0°.15, while a French 'Ver deer' instrument in which these proportions were reversed gave only 0°.08. It remained to manufacture a glass which should have a low depression and at the same time other satisfactory properties. The now well-known glass 16"' is the result. Its composition is shown in the table. The fact that there was an appreciable difference between the scale of the 16"' glass and that of the air thermometer led to further investigation, and another glass, a borosilicate, containing 12 per cent, of boron, was the consequence. This glass has a still smaller depression. As a result of this work Germany can now claim that 'the manufacture of thermometers has reached in Germany an unprecedented level and now governs the markets of the world.'
Previous to 1888 Germany imported optical glass; at that date nearly all the glass required was of home manufacture. Very shortly afterwards an export trade in raw glass began, which in 1898 was worth £30,000 per annum, while the value of optical instruments, such as telescopes, field glasses, and the like, exported that year was over £250,000. Such are the results of the application of science, i. e., organized common sense, to a great industry. The National Physical Laboratory aims at doing the like for England.
The question of standardization of patterns and designs is probably too large a one to go into on the present occasion. Some months ago a most interesting discussion of the subject took place at the Institution of Electrical Engineers. To my mind there is no doubt that the judicious adoption of standard types combined with readiness to scrap old patterns, so soon as a real advance or improvement is made, is necessary for progress. One who has been over some good German
