198 Profs. Liveing and De war. [May 12, 



the beautiful effects produced by the passage from the lower to the 

 higher heat-level, and shows the important bearing on solar physics 

 of the results obtained by this new method of work. 



"In the flame the two least refrangible of the components of b are 

 seen associated with a line less refrangible so as to form a triplet. 

 A series of flutings and a line in the blue are also seen. 



" On passing the spark all these but the two components of b are 

 abolished. We get the wide triplet replaced by a narrow one of the 

 same form, the two lines of b being common to both 



" May we consider the existence of these molecular states as forming 

 a true basis for Dalton's law of multiple proportions ? If so, then 

 the metals in different chemical combinations will exist in different 

 molecular groupings, and we shall be able, by spectrum observations, 

 to determine the particular heat- level to which the molecular complexity 

 of the solid metal, induced by chemical affinity, corresponds. 



" Examples . — None of the lines of magnesium special to the flame 

 spectrum are visible in the spectrum of the chloride either^when a flame 

 or a spark is employed." 



In order to ascertain if this spectrum could be produced at a high 

 temperature in the presence of hydrogen, which element we have 

 already shown to be essential to its production at the atmospheric and 

 at reduced pressures, the series of experiments already mentioned in 

 describing the spark spectrum were made with hydrogen at pressures 

 increasing up to twenty atmospheres. 



On the supposition that this spectrum originates from the formation 

 of some chemical compound, probably formed within certain limits of 

 temperature when vapour of magnesium is in presence of hydrogen, 

 the stability of the body ought to depend largely on the pressure, of 

 the gaseous medium. Like Graham's hydrogenium, this body might 

 be formed at a temperature at which it would under ordinary circum- 

 stances be decomposed, provided the pressure of the hydrogen were 

 correspondingly increased. In fact, it has been shown by Troost that 

 the hydrides of palladium, sodium, and potassium all follow strictly 

 the laws of chemical dissociation enunciated by Deville ; and increased 

 pressure by rendering the compound more stable, provided the secondary 

 effect of such pressure in causing a higher temperature in the electric 

 discharge were not overpowering, ought to conduce to a more continuous 

 and brilliant spectrum of the compound. Conversely, if such a more 

 continuous and brilliant spectrum be found to result, in spite of the 

 higher temperature, from increased pressure, it can only be explained 

 by the stability of the substance being increased with the pressure. 



Now what are the facts ? When the spark of an induction coil, 

 without a Leyden jar, is passed between magnesium electrodes in 

 hydrogen at atmospheric pressure, the flutings in the green are, as 

 before described, always seen, but they are much stronger at the poles 



