224 Scientific Intelligence. 



verdict here, then, is very clearly adverse to the statements that 

 have been made regarding the evaporation of water and the con- 

 densation of aqueous vapor as sources of nitric acid." 



14. On the Electrical Conductivity of Stretched Silver Wires ; 

 by J. G. MacGeegor, M.A., B.Sc— A paper on the above sub- 

 ject, communicated by Prof. Tait to the Royal Society of Edin- 

 burgh on the 3d of January, contained a description of a series of 

 experiments, conducted by the author to iind the effect of stretch- 

 ing on the conductivity of silver wires. The wires were stretched 

 by weights. The measurements of resistance were made by 

 means of a Wheatstone's bridge, the wire under examination be- 

 ing joined up as one of its arms. The dimensions of the wires 

 before and after stretching, were determined by means of cathe- 

 tometer observations and specific gravity determinations. The 

 increase in length and decrease in thickness of the wires, caused 

 by stretching, must of course be attended by a corresponding 

 '"" "- -^-- • ' "^^ ■ to be r ■ ' 



The question to be detei 

 whether there was not also a change produced in their 

 by the change produced by stretching in their molecular state. 

 To get this effect, if it should be present, at its maximum the 

 wires were heated to just below the melting point before the 

 weights were hung on. The results were such as to warrant the 

 statement that if any such change is produced it must be very 

 slight, the difference between the resistances before and after 

 stretching being (when that due to change of dimensions had 

 been allowed for) so small as to be within the limits of observa- 

 tional error. No foimer determinations of this kind have been 

 made for silver wires. For copper, iron and steel, Mousson has 

 found that the change in resistance is not completely accounted 

 for by the change in dimensions. In another respect also silver 

 appears to differ from copper wires. Meik and Murray have 

 found that the total increase in the resistance of copper wires, due 

 to stretchmg, is directly proportional to the weights by which 

 they are stretched. Some of the experiments of this paper show 

 that this is not the case for silver wires. 



15. The Nature of Light, with a general account of Physical 

 Optics; by Dr. Eugei^e Lammel, Professor of Physics in the Uni- 

 versity of Erlangen. With 188 illustrations and a plate of spectra 

 m chromohthography. No. xviii of the International Scientific 

 benes.— This is a very excellent popular treatise, intended to afford 

 an answer to the question "What is the Nature of Light?" A 

 mathematical treatment of the subject is avoided in the text, but 

 simple and concise analytical discussions of the more important 

 topics are given in appendices to the different chapters. It is illus- 

 trated with numerous wood-cuts, many of which are novel and in- 

 geniously devised, but most of them would have been more effec- 

 tive had they been engraved in a style worthy of the book. The 

 work is an admirably clear and well arranged exposition of its sub- 

 ject, and is, in the main, well translated. 



