Experimental Examination of the so-called Storm-glass. 93 



In general the first equation (A) would likewise give two limit- 

 ing equations, so that altogether six such equations would be 

 thus obtained ; but in the present case the first equation gives 

 only 



Ldx dz^ x -Q 



which could have been deduced from the foregoing, and the iden- 

 tical expression = 0. 



The four limiting equations (35) and (36) are, however, just 

 sufficient for the calculation. The theory of elasticity, on the 

 other hand, gives six limiting conditions, whence we are also 

 obliged to assume the formation of longitudinal vibrations in 

 every case of refraction. 



It has been previously mentioned that the hypotheses which I 

 took (in PoggendorfPs Annalen, vol. cxi.) as the basis for the 

 calculation of the diffraction of light, are deducible from our first 

 assumptions (1) and (2). This is possible by the methods here 

 employed, if I multiply the equations (1) by dx and by dxdx, 

 and integrate simply and doubly from #=0 to x=e. The six 

 equations thus obtained express that the components of the vibra- 

 tions, and the differential coefficients in relation to x, are the same 

 on both sides of the plane # = 0. 



[To be continued."! 



XIII. An Experimental Examination of the so-called Storm-glass. 

 By Charles Tomlinson, Lecturer on Physical Science, King's 

 College School, London*. 



THE storm-glass did not, I believe, hold rank as a scientific 

 instrument until it was introduced by Admiral FitzRoy in 

 his useful public labours. In the Report for 1862 issued by the 

 Meteorological department of the Board of Trade, it is stated that 

 " if fixed, undisturbed, in free air, not exposed to radiation, fire, 

 or sun, but in the ordinary light of a well- ventilated room or 

 outer airf, the chemical mixture in a so-called storm-glass varies 

 in character with the direction of the wind, not its force, specially 

 (though it may so vary in appearance only) from another cause, 

 electrical tension. 



" As the atmospheric current veers toward, comes from, or is 

 approaching only from the polar direction, this chemical mixture 



* Communicated by the Author. 



t In Admiral FitzRoy *s ' Weather Book' (1863) it is said "preferably 

 in the outer air." 



