AfML 30, 1915] 



SCIENCE 



643 



rector of the National Committer for the Preven- 

 tion of Blindness, New York. Subject: "Saving 

 Sight and Saving Citizens." Illustrated. 



Thursday evening, April 29, "Conservation of 

 Vision." Mr. Ward Harrison, illumiaating engi- 

 neer, Cleveland, Ohio, representing the Illuinina- 

 ting Engineering Society. Subject: "Eight and 

 Wrong Methods of Interior Illumination." Illus- 

 trated by booths. 



The Eoyal Geographical Society, as we 

 learn from Nature, has received news of Sir 

 Aurel Stein's explorations in Central Asia 

 from April to November, 1914. The expedi- 

 tion started in April from Tunhuang, where it 

 had halted to recruit after the trying cam.- 

 paign in the Lop-nor desert between Turfan 

 and the northern boundary of Tibet. The caye 

 temples of the Thousand Buddhas near Tun- 

 huang were re-visited, and further interesting 

 collections were made. The explorer followed 

 the ancient wall for 250 miles, and found that 

 it was constructed of fascines of reeds or 

 brushwood, admirably adapted to check the 

 wind erosion of the desert sands. Coins, pot- 

 tery and metal fragments found near the sur- 

 face made it possible to define the Chinese 

 frontier posts with accuracy. Beyond the So-lu 

 Hu Valley further remains of the same kind 

 were found. While Sir Aurel Stein was hunt- 

 ing for remains of the Great Tuechi on Indo- 

 Hun culture to the north, his surveyor, Lai 

 Singh, examined the ruined town of Khara 

 Ehoto, and proved that this could be no other 

 than Marco Polo's " City of Etzina," where in 

 ancient times travelers bound for Karakoram, 

 the old Mongol capital, used to lay in supplies 

 for the march across the great desert. Here 

 many Buddhist remains were found, and it 

 was ascertained that the ruin of the city was 

 due to failure to maintain the irrigation 

 system. When he despatched his report Sir 

 Aurel Stein had planned to examine Buddhist 

 ruins round Turfan, while his surveyor was 

 to undertake the exploration of the little- 

 known desert ranges of the Kuruk-tagh be- 

 tween Turfan and the Lop-nor depressions. 



There has recently been issued by the Bu- 

 reau of Standards, of the Department of Com- 

 merce, a paper describing a Wheatstone bridge 

 designed with especial reference to flexibility 



of use in measurements with resistance ther- 

 mometers, and discussing the use thereof. 

 The 'bridge is adapted to use with either the 

 Siemens type or Callendar type of resistance 

 thermometer, or with the potential terminal 

 type of thermometer by the use of the Thom- 

 son double bridge method. The instrument is 

 also arranged so that it may be completely 

 seK-calibrated. The 0.01, 0.001 and 0.0001 ohm 

 decades are secured by varying, by means of 

 dial switches, the shunts on three coils per- 

 manently connected in the measuring arm of 

 the bridge. The sum of the resistances which 

 are permanently connected is 2.5 ohms when 

 the dials are set on zero, so that in order to 

 measure resistances smaller than this a coil 

 of 2.5 ohms is connected in the adjacent arm 

 of the bridge. The entire electrical circuit of 

 the bridge, coils, contact blocks, switches and 

 connectors are totally immersed in an oil- 

 bath thermostat, and special manipulating 

 devices for the links and dials, etc., are pro- 

 vided. Details of construction are shown by 

 photographs and briefly explained in the text. 

 A new form of hermetically sealed coil, suit- 

 able for Wheatstone bridges, potentiometers, 

 and similar apparatus, is fully described and 

 record of its performance reviewed. Such 

 construction eliminates the seasonal varia- 

 tions of resistance (with varying atmospheric 

 humidity) found in coils of the usual types. 

 The accuracy attainable with the bridge is 

 such that resistances of one ohm or more can 

 be measured to an accuracy of one part in 

 300,000 in terms of the unit in which the cali- 

 bration is expressed. This corresponds to an 

 accuracy of about 0°.001 for measurements 

 with the platinum resistance thermometer. 

 Low resistances, the accuracy of measurement 

 of which is limited by variations in contact 

 resistances, may be measured to about three 

 millionths of an ohm. This figure, rather than 

 the one given above for accuracy, represents 

 the precision attainable in measuring small 

 changes of resistance such as are usual in 

 resistance thermometry. 



The nation-wide study of the lumber indus- 

 try, which is being made jointly by the Depart- 

 ment of Agriculture and the Department of 



