572 Scientific Intelligence. 



For the vapor of ethyl bromide' came out equal to 16'4. The 



* . p 



values of this ratio for solid bromine, in the compounds sodium 



bromide and bromyl hydrate, were respectively 16-2 and 16-3. 



The agreement between the value of - for the vapor and for the 



" P 



solid is about as good as could be expected from the nature of the 

 experimental method. In the case of iodine in the solid condi- 

 tion and as present in the molecules of the vapor of methyl iodide, 



the ratio — was found to have the same value, viz., 2*3. 

 P 



" Although it has only been proved in these two cases that ele- 

 ments in the solid and vapor state emit the same type of radia- 

 tion, yet it is safe to conclude that what applies here holds 

 generally ; especially considering that the atomic weights of bro- 

 mine and iodine are well separated." " It is evident that this 

 similarity of character in the radiations is what would follow 

 from the fact that the phenomena of secondary X-rays are atomic 

 in their nature." 



Some other experiments are described in the paper, which are 

 interpreted as showing that the hypothesis which regards the 

 characteristic secondary radiation as resulting from the subse- 

 quent bombardment of atoms by ejected corpuscles is quite 

 untenable. However, for further details in this connection refer- 

 ence must be made to the original article. — Phil. Mag. (6), xxi, 

 446. h. s. u. 



8. Lehrbuch der Kristallphysik ; von Dr. Wolbemar Voigt. 

 Pp. xxiv, 964 ; 213 text-figures, 1 plate. Leipzig and Berlin 

 (B. G. Teubner, Sammlung von Lehrbiichern, Band xxxiv). — This 

 is an encyclopaedic work upon the physical properties of crystals, 

 omitting, however, their optical properties. The first chapter 

 deals with the geometrical properties of crystals and the applica- 

 tion of the principles of symmetry ; the second and third chapters 

 give an account of the vectorial analysis which is used by the 

 author and of the mechanical and physical principles which find 

 application later. The remaining five chapters deal with physi- 

 cal properties, such as pyro-electricity and pyro-magnetism, 

 thermal expansion, conductivity for heat and electricity, thermo- 

 electric and thermo-magnetic effects, elasticity and viscosity, 

 piezo-electricity and piezo-magnetism. The classification of 

 these effects is based upon their mathematical analogies — as to 

 whether they involve a scalar and a vector, two vectors, etc. 



It would be difficult for any one who has not paid especial 

 attention to this intricate and rather recondite branch of physics 

 to give an intelligent opinion upon a work like the present, which 

 is very voluminous and abounds in details. It is quite certain 

 that there is no one better qualified than Prof. Voigt to write a 

 treatise upon this subject, which he has long made his own ; 

 and it is probable that this book will long remain the standard 

 in its field. h. a. b. 



