390 Scientific Intelligence. 



Unless the ether is immovable under the mechanical forces in a 

 varying electro-magnetic field, there are a multitude of phenom- 

 ena awaiting discovery. If the ether does move, then the velocity 

 of transmission of electrical vibrations, and therefore of light, 

 will be affected by a steady magnetic field. Such a field, even if 

 containing nothing but ether, will behave towards light like a^ 

 crystal, and the velocity of propagation will depend upon the 

 direction of the rays. A similar result would also hold in a 

 steady electric field. We may hope that experiments on these 

 and similar points may throw some light on the properties of that 

 medium which is universal, which plays so large a part in our 

 explanation of physical phenomena, and of which we know so 

 little. 



11. Absolute hardness. — F. Aueebach shows that the method 

 proposed by Hertz, and worked out by himself, of determining 

 absolute hardness by the optical method, employing lenses and 

 plates of the material in question, and finding what pressure of 

 the one upon the other just brings about disintegration, is capable 

 of great exactness and consistency. Special precautions must be 

 observed to distinguish between the sources of error afiecting 

 brittle bodies and those affecting plastic ones. In the case of 

 crystals it is necessary to define which face is operated upon. The 

 best surface to choose is that of cleavage. The numbers obtained^ 

 expressed in kg. per sq. mm., show that Mohs's scale is far from 

 giving a uniform succession of values. Talc figures at 5, but it is 

 untrustworthy, and it should also be preceded by wax and 

 graphite, aud followed by gypsum, 14. Rock-salt is 20. Between 

 this and calc-spar (92) there is a great gap, which might well be 

 filled up by sylvine, glauberite, and galena. Fluorspar is 110. 

 Then comes another gap, which should be filled up with scheelite, 

 heaviest silicate flint-glass (1*70), and light flint-glass (210). Then 

 comes apatite (237), followed closely by adularia (253), which 

 might be succeeded by borosilicate crown glass (274). Quartz, 

 topaz, and corundum figure at 308, 525, and 1150 respectively ; 

 and diamond is not as yet determined. — Wied. Ann., Iviii, 357 ;, 

 Proc. Phys. /Soc, xiv, 296. 



12. Determination of Freezing Points ; by J. A. Haeker. 

 (Abstract from the Proc. Roy. Soc, Ix, 154.) — Of recent years 

 great improvements have been made in the construction of accu- 

 rate thermometers. For their graduation and study, the position 

 of the thread for at least two fixed temperatures must be known 

 with certainty, and one of these is generally the freezing point. 

 According to many observers, the methods at present in use for 

 the determination of this point are unsatisfactory and cannot be 

 relied on, even when considerable precautions are taken, to more 

 than about 0-001° to 0'002°. The object of the present com- 

 munication is to describe a method by which more consistent 

 results can be obtained, and which is applicable to all kinds of 

 thermometers. 



The method adopted is to cool distilled water in a suitable 



