162 Supposed Effects <xf a Waterspout. 



CONTRACTIONS PRODUCED BY HEAT IN CRYSTALS. 



M. Mitscherlich has observed that the mutual inclination 

 of the faces of Iceland spar varied in a perceptible manner by 

 the effect of heat, and that between 0° and 100°, the change 

 of the dihedral angles at the extremities of the axis of the 

 rhomboid amounted to 8V. It thence results, that supposing 

 no dilatation to take place perpendicular to the axis of the cry- 

 stal, its cubical dilatation would still surpass that of glass, by 

 nearly one half; but, in measuring the cubical dilatation of 

 Iceland spar with M. Dulong, M. Mitscherlich found that it 

 was on the contrary less than that of glass ; which leads to this 

 singular result, that though heat dilates the crystal in a direc- 

 tion parallel to its axis, it must cause its molecules to approach 

 in the perpendicular directions. This M. Mitscherlich has also 

 confirmed by measuring with a spherometer, at different tem- 

 peratures, the thickness of a plate of Iceland spar cut parallel 

 to the axis. 



It is very probable that sulphate of lime would present 

 an analogous but inverse phenomenon; namely, that the eleva- 

 tion of temperature would produce a perceptible contraction 

 in the direction of its axis. (A. F.) — Ann. de Chim. xxvi. 222. 



DIRECTION OF THE AXES OF DOUBLE REFRACTION IN CRYSTALS. 



It is known that the optical axes of the crystals improperly 

 called crystals with two axes, do not coincide with the axes of 

 crystallization; but hitherto it has been regarded as a general 

 rule, that the right lines which divide the angle contained be- 

 tween these optical axes into two equal parts must be equally 

 inclined on the corresponding faces of the crystal. M. Mit- 

 scherlich has ascertained that these lines of symmetrywith rela- 

 tion to the double refraction, are not always so as regards 

 the faces of the crystal ; and that in some salts, such as the 

 sulphate of magnesia, they incline more to one side than to 

 the other, without any defect of symmetry in the crystalline 

 forms giving cause a priori to suspect such a deviation. (A. F.) 

 — Ann. de Chim. vol. xxvi. p. 223. 



SUPPOSED EFFECTS OF A WATER-SPOUT. 

 Gentlemen, Strathinday Bleaclifield, July 8, 1S24. 



My servants observing the particular attention I have paid 

 to the meteorological phenomena of Loch Leven, its sur- 

 rounding morass and mountains, for years back have been on 

 the alert to bring me the earliest notice of every change, or 

 the first appearance of any cloud, or vapour, likely to produce 

 an indication of phenomena worth remarking. 



One of them came the other morning, wearing a physiog. 

 fraught with matter of importance, told me, he was certain we 



were 





