NOVEMBEE23, 1900.] 



SCIENCE. 



781 



optical glass smelting was a German, to wit 

 Fraunhofer. His untimely death was fol- 

 lowed by a long period of stagnation, and 

 the limits of the possible were soon reached 

 when attempts were made to construct very 

 large objectives, at least as far as the op- 

 tician's art was concerned. About twenty 

 years ago, Professor Abbe and Dr. Schott, 

 of Jena, resumed the thread where Fraun- 

 hofer had left off, and they succeeded in 

 producing the old crown and flint-glasses ia 

 such perfection that the chromatic differ- 

 ences of spherical aberration can be com- 

 pensated almost completely. This led to 

 great improvements in telescope lenses, and 

 at the same time the Jena Glass Works 

 have become so productive as to enable 

 German opticians to cover their entire de- 

 mand in Germany. Great progress has also 

 been made in such an important branch of 

 manufacture as that of spirit-levels. Not 

 onlj' are the finest spirit-levels incon- 

 testably made in Germany, but, in addi- 

 tion, the Imperal Physical and Technical 

 Institute has successfully investigated the 

 causes of the formation of deposits within 

 the levels. Mechanicians possess now a 

 ready means of detecting glass liable to de- 

 terioration and have no difiBculty in secur- 

 ing suitable glasses. 



III. The third section, comprising geo- 

 metric and nautical instruments, includes 

 also those instruments which form a con- 

 necting link between astronomy proper and 

 the land-surveyor's art, i. e., those astro- 

 nomical instruments which are employed 

 for geodetic measurements. Many improve- 

 ments in this group of instruments have 

 emanated from German workshops and have 

 had their origin in the requirements of the 

 International Survey and especially the in- 

 fluence of the Geodetic Institute and its 

 present director. Dr. Helmert. We may 

 here mention the conversion of the friction- 

 rollers of transit instruments into a bal- 

 ance beam, so as to completely compensate 



the errors of collimation. We may also 

 refer to Eepsold's mode of fitting transit 

 instruments so as to neutralize almost en- 

 tirely the personal equation, and equally 

 important are the improvements in zenith- 

 telescopes and spirit-level testing appli- 

 ances. The geophysical investigations of 

 the International Survey have given birth 

 to the most sensitive instrument of our 

 times, the horizontal pendulum, which owes 

 its origin and development to German sci- 

 entists and mechanicians. The study of 

 the movements of the oceans has recently 

 been facilitated by greatly improved instru- 

 ments, the most perfect of which are those 

 of Seibt-Fuess. Remarkable progress has 

 in late years been made in the construction 

 of surveying instruments. The require- 

 ments of surveyors and engineers have 

 reached such a high stage of development 

 that they could not fail to beneficially affect 

 the construction of theodolites, leveling in- 

 struments and tacheometers. The manu- 

 facture of surveying instruments is carried 

 on in Germany on a very extensive scale, 

 and the reputation of these instruments 

 has obtained for them a wide market all 

 over the world. Considerable improve- 

 ments have also been made in small com- 

 pactly built surveying instruments, which 

 have been requisitioned by numerous Ger- 

 man explorers. As the natural outcome 

 of the developments of the merchant ser- 

 vice and the creation of a powerful navy, 

 considerable attention is paid to the manu- 

 facture of nautical instruments. Whereas 

 formerly Germany depended for these ac- 

 cessories of navigation upon other coun- 

 tries, England in particular, at the present 

 time all nautical instruments are manufac- 

 tured at home equally well, in some- re- 

 spects even better than abroad. 



IV. 'The development of the meteoro- 

 logical instruments and the appliances for 

 measuring temperatures presents a typ- 

 ical illustration of the close connection be- 



