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SCIENCE. 



[N. S. Vol. XII. No. 308. 



tween theoretical science and manufacture 

 in Germany. This applies in particular to 

 thermometers. About twenty years ago 

 the manufacture of thermometers had come 

 to a dead stop in Germany, thermometers 

 being then invested with a defect, their lia- 

 bility to periodic changes, which seriously 

 endangered German manufacture. Com- 

 prehensive investigations were then carried 

 on by the IvTormal-Aichungs-Kommission, 

 the Imperial Physical and Technical Insti- 

 tute and the Jena Glass Works, and after 

 much labor brought the desired reward. 

 Chemical analysis in conjunction with care- 

 fully managed glass smeltings and practical 

 tests showed that pure potassic and pure 

 sodic glasses possess these defects in the 

 least degree, whereas glasses containing 

 both alkalis are subject to periodic changes 

 to such an extent as to render them useless 

 for thermometric purposes. The last out- 

 come of these investigations was the pro- 

 duction, at the Jena Glass Works, of an 

 excellent sodium glass which shows depres- 

 sions of not more than 0.1° per 100°. Re- 

 cently a boro-silicate glass has been pre- 

 pared which shows a maximum depression 

 of only 0.05° and possesses, moreover, 

 the important property of excellently agree- 

 ing with the hydrogen thermometer. The 

 advantages which may result from these 

 discoveries to meteorology as well as the 

 physical, chemical and medical sciences, 

 are obvious. The technical arts too have 

 benefited by discovery. With the aid of 

 the new glasses and the invention of a 

 process by which mercury is kept in the 

 thermometer under a pressure of from 20 

 to 25 atmospheres, thermometers have been 

 constructed for temperatures up to and be- 

 yond 550° C, as far as the region of in- 

 cipient red heat, and reading accurately to 

 ^°. In consequence of these systematic 

 efforts the manufacture of thermometers has 

 reached in Germany an unprecedented 

 level, and now governs the market of the 



world. German thermometers are pur- 

 chased everywhere with particular confi- 

 dence, as they can be supplied with ofiQcial 

 certificates. The Thermometer Testing In- 

 stitute of Ilmenau examine annually about 

 40,000, and 16,000 are annually tested by 

 the Imperial Physical and Technical Insti- 

 tute. German barometers, mercurial as 

 well as aneroid, enjoy a high reputation and 

 are everywhere esteemed for their delicate 

 workmanship and reliability. The aneroid- 

 barometers, which have obtained increased 

 importance through the requirements of ex- 

 plorers, are tested by the Imperial Physical 

 and Technical Institute with respect to 

 their liability to periodic changes. The 

 merits of the German self-registering in- 

 struments of the Sprung-Fuess type, ther- 

 mographs and barographs, anemometers and 

 rain-gauges are so well known that they 

 need no further comment. These excellent 

 instruments are used in all the meteorolog- 

 ical observatories of the world. Finally, 

 attention should be drawn to the pyrome- 

 ters and calorimeters, which have also been 

 considerably improved in recent years. 



V. Like the mechanical arts, optical 

 construction has made great and rapid 

 progress in Germany. In this connection it 

 is our gratifying duty to mention the name 

 of Abbe, whose master-mind has had a 

 profound influence upon the development 

 of German optical science and manufacture. 

 Abbe's earliest great merit is the elucidation 

 of the theory of the microscope, by which 

 he has placed microscopical optics upon an 

 entirely new basis. It is also due to his 

 efforts, in conjunction with those of Dr. 

 Schott, the head of the Jena Glass Works, 

 that numerous optically valuable glasses 

 have been rendered available for the pur- 

 poses of optical construction and that many 

 difficult problems have now been solved. 

 The new Jena phosphate and baryte glasses 

 have led to many improvements in micro- 

 scopical optics. We need only refer to the 



