THE ADVANCE OF SCIENCE 89 



transference over long distances at present discovered or 

 laid bare to experiment and observation. 



High and low temperatures. The past quarter of a 

 century has witnessed a great development and applica- 

 tion of the methods of producing both very low and very 

 high temperatures. Sir James Dewar, by improved 

 apparatus, has produced liquid hydrogen and a fall of 

 temperature probably reaching to the absolute zero. A 

 number of applications of extremely low temperatures to 

 research in various directions has been rendered possible 

 by the facility with which they may now be produced. 

 Similarly high temperatures have been employed in con- 

 tinuation of the earlier work of Deville, and others by 

 Moissan, the distinguished French chemist. 



Progress in Chemistry. In chemistry generally the 

 theoretical tendency guiding a great deal of work has 

 been the completion and verification of the ' periodic law ' 

 of Mendeleeff; and, on the other hand, the search by 

 physical agents such as light and electricity for evidence 

 as to the arrangement of atoms in the molecules of the 

 most diverse chemical compounds. The study of 

 * valency ' and its outcome, stereo-chemistry, have been 

 the special lines in which chemistry has advanced. As a 

 matter of course hundreds, if not thousands, of new 

 chemical bodies have been produced in the laboratory of 

 greater or less theoretical interest. The discovery of the 

 greatest practical and industrial importance in this con- 

 nection is the production of indigo by synthetical pro- 

 cesses, first by laboratory and then by factory methods, so 

 as to compete successfully with the natural product. 

 Von Baeyer and Heumann are the names associated with 

 this remarkable achievement, which has necessarily dis- 

 located a large industry which derived its raw material 

 from British India. 



