378 Analyses of Books. . [Nov. 
the electricity produced by the friction of the mercury against 
the glass was discharged through the vapour with sparks so 
bright as to be visible in day-light. 
When the minutest quantity of rare air was introduced into 
the mercurial vacuum, the colour of the electrical light changed 
from green to sea-green, and by increasing the quantity, to blue 
and purple: in low temperatures, the vacuum became a much 
better conductor. 
The results were precisely the same, when a difficultly fusible 
amalgam of mercury and tin was used as when pure mercury was 
employed, and in a vacuum above fused tin, the same phenomena 
were also exhibited. Electrical and magnetic repulsions and 
attractions took place as they would have done in air. It was 
ascertained ‘that the feebleness of the light in the more 
perfect vacuum was not owing merely to a smaller quantity of 
electricity passing through it; for the same discharge which 
produced a faint green light in the upper part of the tube, pro- 
duced a bright purple light in the lower part, and a strong spark 
in the atmosphere.” 
Pure olive oil and chloride of antimony were severally tried in 
the vacuum, and it was found “ that the light produced by the 
electricity passing through the vapour of the chloride was much 
more brilliant than that produced by it in passing through the 
vapour of the oil; and in the last it was more brilliant than in 
the vapour of mercury at common temperatures: the lights ~ 
were of different colours, being of a pure white in the vapour of 
the chloride, and of a red, inclined to purple, in that of the oil ; 
and in both cases permanent elastic fluid was produced by its 
transinission.” 
Sir H. Davy observes, “ The law of the diminution of the 
density of vapours by diminution of temperature has not been ac- 
curately ascertained ; but I have no doubt, from the experi- 
ments of Mr. Dalton, and some I have made myself, that it is 
represented by a geometrical progression ; the decrements of 
temperature being in arithmetical progression ; and in three pure 
fluids that I operated upon (water, chloride of phosphorus, and 
sulphuret of carbon), the ratio seemed nearly uniform for the 
same number of degrees below the boiling point ; and (taking 
intervals of 20 degrees of temperature) -369416. Upon this 
datum, Sir Humphry was obliged to Mr. Babbage for the calcu- 
lation, that considering the elastic force of vapour of water at 
52° to be equal to raise by its pressure about -45 of an inch of 
mercury; the relative strengths of vapour will be, reckoning the 
boiling points all from 52°, for mercury at 600°, 000015615; for 
oil at 540°, 0016819; for chloride of antimony at 340°, 01692 ; 
and for tin at 5000°, 37015 preceded by 48 zeros. These num- 
bers are given to show how minute the quantity of matter must 
be in vapours where its effects are distinct upon electrical phe- 
