278 Chronicles of Science. [April? 



deduce that the mean of the readings of the azimuths, which should 

 strictly differ by 180°, gives, after the subtraction of 90°, the real 

 azimuth. The error is eliminated of its own accord, if we choose 

 for the measurements of the azimuths the mean of two positions of 

 extinction, whether for the analyzer or for the polarizer. 



M. E. Javal has described a new instrument which he calls the 

 Iconoscope, intended to give relief to plane images examined with 

 the two eyes. From the 'description we judge that this is an instru- 

 ment similar to one which has long been known in England. It 

 consists of an arrangement of prisms so placed that each eye 

 receives an impression from the same point of view. On looking 

 through the instrument at a picture, the eyes always preserving the 

 same amount of convergence and being thereby unable to judge 

 that the objects are on a flat surface, the painting has a semblance 

 of relief. 



Heat. — In the second part of a memoir " On the Changes of 

 Temperature produced by the Mixture of Liquids of different 

 Natures," recently published by Messrs. Bussy and Buignet, the 

 following very important conclusions are arrived at : — 1. In all the 

 cases under examination, with one sole exception, the calorific capa- 

 city of the mixture is a little superior to the mean capacity of the 

 elements. 2. By a singular opposition, the liquids for which the 

 increase of bulk is the most considerable, are exactly those which 

 develop most heat at the moment of their union, such as ether and 

 chloroform, alcohol and water, sulphuric acid and water. Mean- 

 while, the only instance hitherto noticed of diminution of bulk is 

 the mixture of chloroform and sulphide of carhon, the decrease of 

 temperature taking place at the moment of the union. 3. Inde- 

 pendently of the loss of heat resulting from the changes of 

 volume, there exists a cause which produces alone an absorption 

 of heat — an absorption which can be sometimes equal and even 

 superior to the heat given oat by the combination of the liquids. 

 This cause, perhaps, may proceed from the separation of the 

 homogeneous particles necessary for the diffusion of the liquids. 



M. Fizeau has continued his researches on the dilatation of 

 crystals. He has experimented upon several series of salts present- 

 ing a great analogy with each other — such as chlorides, bromides, 

 and iodides — expecting that this analogy would be manifested by the 

 manner in which crystals are influenced by the action of heat. His 

 previsions are in general confirmed, and in the course of his studies 

 he has discovered a singular anomaly, and one which constitutes a 

 real discovery. "While the coefficient of dilatation of all the 

 chlorides, bromides, iodides, is positive, in the same manner as it 

 is for all substances experimented upon up to the present day, the 



